1

Chapter 5

Flora

AQUATIC MACROPHYTES

Major changes have occurred in the flora of the Nile system in Egyptian Nubia in recent years, following the completion of the Aswan High Dam in 1964. In 1963, the area of the Nile Valley which was to become Lake Nasser had a relatively rich submerged and emergent flora (57 species, of which 6 were euhydrophytes) before the construction of the Aswan High Dam (AHD) (Boulos 1966). After the construction of AHD, Springuel & Murphy (1991) during 1980-1986 recorded 9 species of euhydrophytes, while Ali (1987) recorded 7 species only. Changes in aquatic vegetation may be due to changes in the water level regime and/or changes in the physico-chemical factors following waterbody regulation (Ali et al. 1995). The latter author discussed the effect of physico-chemical factors of both water and hydrosoil on the distribution of macrophyte vegetation in the River Nile in Upper Egypt (Lake Nasser, Aswan Reservoir and the Nile).

Erosion of the littoral zone is a natural phenomenon occurring in regulated bodies and is often linked closely with wave action (Smith et al. 1982). Ali et al. (1995) show that the littoral zone of Lake Nasser is characterised by a coarse hydrosoil texture, which may be formed due to the water level fluctuation and exposure to waves. As a result of the construction of the AHD, the new littoral zone of Lake Nasser has mainly a sandy substrate, as the submerged area was previously a desert. Most of the silt which had been brought by the floods, was accumulated behind the dam. Such accumulation of silt, in the north section of the Lake, gave a hydrosoil texture of clay loam. This texture is reflected in the species composition, being similar to that of the southern section of Aswan Dam. Thus, abundant growth of Najas horrida was recorded in both zones. Some of the silt was deposited on the shores and khors on both sides of the Lake. Due to the water level fluctuation and wave action, the

2

accumulated silt is washed from the banks and accumulated in the main channel, leaving behind sandy or sandy loamy sand banks where Potamogeton lucens (= P. schweinfurthii) and Najas marina subsp. armata are the dominant plants.

It seems that the abundance of a species differs with different water level fluctuation regimes. An extended range of water level fluctuation results in the mortality of aquatic vegetation caused by the absence of low light conditions (Rorslett 1989). Therefore, extreme changes in water levels give rise to communities that are extremely species poor or absent and so the littoral zone is impoverished (Smith et al. 1982).

Springuel & Murphy (1991) pointed out that habitat disturbance appears to be an important pressure acting upon the macrophyte population in Lake Nasser. The littoral zone is prone to massive disturbance, caused by water level fluctuations. Marginal beds of macrophytes may be exposed to the air (and to extreme heat and aridity), or submerged deep in the water column, at irregular intervals during the year, with potenially catastrophic impact on established plant populations. Murphy et al. (1990) showed that all macrophyte species ocurring in Lake Nasser show a strong element of disturbance-tolerance traits in their strategy type.

The highest amplitude of water level fluctuation in Lake Nasser was

recorded in 1988, during the drought period. The mean monthly level of the

Lake dropped to as low as 150.62 m above mean sea level on 20 th and 21st

July, 1988, about 30.68 m lower than the maximum level of the Lake in 1998

(181.30 m MSL). First, continuous low water level exposed the littoral

shallow water habitats, and submerged macrophytes became exposed and

desiccated. Following this, a period of continuous high water level caused

low-light conditions for the same area of the littoral zone. The occurrence of

these two events in a short period caused substantial mortality of the

submerged aquatic plant communities during the drought period in 1988

(Ali et al. 1995). The initial community has Najas horrida A.Br.ex Magn. as the

dominant species, with six other species present (Ali 1987). Following the

destruction of that community, Najas marina L. subsp. armata (Lindb.) Horn

became dominant, with four other taxa present (Najas horrida, Zannichellia

palustris L., Vallisneria spiralis L. and Potamogeton schweinfurthii A. Benn.) (Ali

et al. 1995).

Euhydrophyte species The following represents the submerged hydrophytes (euhydrophytes -

flowering and non-flowering) recorded in Lake Nasser.

1- Najas marina subsp. armata (Lindb.). Until recently this plant was restricted in

Egypt, to the Nile Delta, Fayoum, the Mediterranean coastal strip, Isthmic

region, and Oases of the Western Desert (CAI*, Täckholm 1974). In 1973, it was

* CAI=Cairo University Herberium

3

recorded in Lake Nasser by El-Hadidi (1976), and Entz (1976). This species has

subsequently spread vigorously in Lake Nasser and, to a lesser extent, other

waters in Egyptian Nubia (Triest 1988). Najas marina subsp. armata is currently a

dominant species in Lake Nasser, showing vigorous growth throughout the

Lake littoral region during 1980-86 (Belal et al.1992). In 1988-89, it made up

about 40% of the total standing crop. Najas marina occurs mainly in Lake

Nasser, characterized by alkaline water and high electrolyte concentration. It

grows on sand, clay, silt, clay with shells and thick organic matter. In most cases

Najas marina is observed on an organic substrate covered with a layer of sand or

clay. Though the tendency to form extensive pure stands, inhibiting

colonization by potential competitors is characteristic of Najas, most species are

of local occurrence (Ali et al. 1995). However, with respect to their vigorous

growth and individual seed production, the biotic importance of Najas as a

source of food for many sorts of waterfowl should not be underestimated.

2- Najas horrida A. Br. This species was confined to Lower Egypt and the oases

prior to the filling of Lake Nasser, although specimens in CAI* are confused

with Najas pectinata (Parl.) (Täckholm 1974, Triest 1988). It has now become

abundant in the shallow waters of numerous khors (inundated wadis and side-

arms) of Lake Nasser, often codominant with Najas marina subsp. armata (Belal

et al. 1992). Najas horrida shows considerable morphological plasticity in its

general habitat which may be robust, with curved rigid leaves or slender with

straight lax leaves. Concerning the plasticity of Najas horrida, there could be a

relationship between very compact specimens and the total mineralization of

the water.

3-Vallisneria spiralis L. This species was recorded from the Aswan High Dam

(Abdallah et al. 1972). It was also reported in 1968 by El-Hadidi & Ghabbour

(1968) from three separate locations around Aswan. It remains common in all

Nubian waters, including both major impoundments, and the river north of the

two Dams (Belal et al. 1992). Ali (1987) pointed out that this rooting hydrophyte

grows in shallow waters of many khors in both sides of Lake Nasser.

4- Zannichellia palustris L. This species is widespread in Egypt, occurring in the

Nile Valley, Mediterranean, Isthmic and Oases regions (CAI and Täckholm

1974). In Egyptian Nubia it was recorded by El-Hadidi & Ghabbour (1968) in

the Aswan Dam Area (CAI) and by Täckholm (1974) from irrigation canals near

Allaqi village (CAI). Other records confirm that the species was present pre-

1964 in water courses in the Upper Nile Valley, subsequently inundated by

Lake Nasser (Abdallah et al. 1972, Boulos 1966, El-Hadidi 1976, El-Hadidi &

Ghabbour 1968). It remains quite widespread in Egyptian Nubia, including

Lake Nasser, but does not form dense stands (Springuel 1981, 1985 a and b).

4

This tiny submerged hydrophyte was recorded in very shallow khors in the

southern region of the Lake (Ali 1987).

5- Potamogeton lucens L. (= P. schweinfurthii A. Benn.). This species was found to

be very rare in the Nile Delta, eastern Mediterranean coastal region, and

Isthmic regions (Täckholm 1974). Small stands of this species were recorded by

Springuel as Potamogeton nodosus in 1980 in Lake Nasser near Khor Kalabsha, in

the northern sector of the Lake. Later, Ali (1992) proved it was an abundant

growth of P. lucens in the same area.

6- Potamogeton crispus L. Records in CAI and Täckholm (1974) suggest that this

species has long been widespread in Egypt: common in the lower Nile, Sinai,

the Isthmic Desert, Mediterranean region, and Oases. The plant was recorded

from the Nile at Edfu, Kom Ombo, Aswan, and the Aswan Reservoir (CAI). Its

presence in the Nile in Egyptian Nubia prior to construction of the Aswan High

Dam was reported by many authors (Abdallah et al. 1972, Ahti et al. 1973,

Boulos 1966 and El-Hadidi & Ghabbour 1968). The plant remains were common

in the Nile downstream of the Aswan Dam. It was not recorded during the

early years of the formation of Lake Nasser (Entz 1976), but was slowly

invading the impoundment, being first recorded by Imam (CAI). Beds of P.

crispus were confirmed as present in the northern sector of the Lake in 1979 by

Springuel. Ali (1987) pointed out that this submerged hydrophyte was rare in

the southern region of the Lake, confined to khors with shallow water and slow

current. In later surveys this species was not recorded, and it may have been

lost from the Lake (Belal et al. 1992).

7- Potamogeton pectinatus L. A widespread aquatic weed of irrigation and

drainage canals in the Nile Delta. P. pectinatus also occurs in the River Nile

valley, Oases, Mediterranean and Isthmic Desert regions of Egypt (CAI,

Täckholm 1974). The presence of the plant in Egyptian Nubia before the

construction of the Aswan High Dam is confirmed by several reports (Abdallah

et al. 1972, Ahti et al. 1973, Boulos 1966, El-Hadidi 1976 and El-Hadidi &

Ghabbour 1968). Entz (1976, 1980b) pointed out that the spread of macrophytes

on a large scale in Lake Nasser started in 1972-73, with the development of

stands of P. pectinatus in shallow sandy areas of the Lake. P. pectinatus was

more common in the southern than in the northern sectors of Lake Nasser.

Potamogeton pectinatus shows phenotypic changes in growth, so that

photosynthetic tissue production is maximized near the water surface under

varying water levels. This plant was not observed in the Lake during recent

years (Belal et al. 1992).

8- Potamogeton trichoides Cham. & Schlecht. The first record of this species in

Egypt was in May 1962 by Täckholm and El-Hadidi, from irrigation

channels near Aswan. The plant was recorded in Lake Nasser in 1978 by

5

Imam in Khors Tushka and El-Malki (CAI). During 1981-82 it was abundant

in the northern sector of the Lake (Springuel 1985b). Between 1982-87, the

major fall in water coincided with the disappearance of P. trichoides from the

northern sector, although it remained as a rare species in the southern sector

of the Lake, near the Sudanese border. However, recent surveys showed that

P. trichoides could have disappeared from the Lake (Belal et al. 1992).

9- Potamogeton perfoliatus L. It is found in canals in the Nile near its banks. It

was discovered for the first time in Egypt by Täckholm in 1951 growing in

the recently constructed freshwater reservoir 'Sadd el Rauwafaa' in northern

Sinai. Before inundation by Lake Nasser, it was discovered in the Nile at

Abu Simbel and Ballana (Boulos 1966).

10- Nitella hyalina (DC) Agardh. This macroalga grows in Lake Nasser, not to

any great depth, in open sunny locations (Ali 1992). It has a cosmopolitan

distribution. Although it is known from many parts of the world, it is rare in

Lake Nasser. This species often grows on calcareous sand at lake edges

(Belal et al. 1992). The presence of the species was reported in 1972-73 by

Entz (1980b) but misidentified as Chara sp.

11- Myriophyllum spicatum L. This species is often described as an invasive

species, and it is loosely accepted that invasions are frequently followed by

rapid concomitant displacement of native species (Smith & Barko 1990).

Myriophyllum spicatum has been discovered in the Nile valley during the

past decade and its rapid colonisation seems to be influenced by changes in

the Nile water regimes after the building of the AHD (Fayed 1985).

Optimal growth of Myriophyllum spicatum occurs in alkaline (hard-

water systems) with concomitantlly high concentrations of dissolved

inorganic carbon (Spence 1967, Hutchinson 1957 and Stanley 1970). Smith &

Barko (1990) point out that water alkalinity provides a simple, but useful

measure of the growth potential of Myriophyllum spicatum. This species

appeared in Lake Nasser in 1993, probably introduced into the Lake through

fishing nets contaminated with this hydrophyte, which were previouslly

used in the Nile downstream (personal communication, Ali 1998).

6

Belal et al. (1992) classify the above mentioned species into two groups:

a. Cosmopolitan species. Potamogeton crispus, P. pectinatus, Najas marina subsp.

armata, Zannichellia palustris and Nitella hyalina are recorded worldwide,

including a range of countries in North Africa and Middle East (CAI, Andrews

1965, Mouterde 1966, Dandy 1937, Quézel & Santa 1962, Triest 1988, Van

Vierssen 1982). Their presence in Upper Egypt is to be expected, but became

abundant in this area as a result of new or modified habitats due to the

construction of the Aswan High Dam (Belal et al. 1992).

b. Subcosmopolitan species. Potamogeton trichoides has long been known from

Western North Africa and East Africa (Dandy 1937, Maire 1952), as well as

Turkey and Palestine (Dismore 1933), Syria and Lebanon (Mouterde 1966).

Vallisneria spiralis is more typically a tropical/subtropical species (Lowden

1982), rare in Africa as a whole, but associated with the Nile system (El-Hadidi

1968). Najas horrida occurs throughout tropical Africa and Madagascar (Triest

1988).

Changes in the macrophyte flora of Egyptian Nubia over the time

Historically, Lower Egypt has been considered the hub of freshwater

macrophytes distribution in Egypt as shown by the prevalence of herbarium

records in CAI and literature records (e.g. Simpson 1932, Täckholm & Drar

1950, Täckholm 1974). Intensive botanical surveys of the Nile Valley in Egyptian

Nubia prior to its inundation by Lake Nasser, revealed the presence of a limited

number of aquatic macrophytes species (euhydrophytes) (Table 39).

In Lake Nasser, during 1963-1964, Boulos (1966) recorded Alisma

gramineum, Damasonium alisma Mill var. compactum Michell, Potamogeton crispus,

Potamogeton pectinatus, Zannichellia palustris and Potamogeton perfoliatus (which

was a new record). In 1972, Potamogeton pectinatus (Entz 1976), and in 1973-1974

Najas marina subsp. armata, N. horrida, Z. palustris and Potamogeton pectinatus

were recorded (El-Hadidi 1976, Entz 1980b). In 1981-1982 Springuel (1985b)

recorded Najas marina subsp. armata, Najas horrida, Potamogeton trichoides, P.

crispus, Zannichellia palustris, Vallisneria spiralis and Potamogeton lucens (which

was identified as P. nodosus).

During 1980-1986 Springuel & Murphy (1991) recorded 9 species of

euhydrophytes (Table 39). Najas armata and N. horrida were abundant in the

shallow waters along both shorelines of the Lake, abundantly associated with

Vallisneria spiralis. Less commonly associated with Najas-Vallisneria community

were Zannichellia palustris, Potamogeton trichoides and P. crispus. In contrast V.

spiralis showed pronounced increase mainly in the mid sector of the Lake

during the study period. Zannichellia palustris and Potamogeton species tended to

7

be most abundant in the southern sector of the Lake (>200 km south AHD),

even raplacing Najas spp. as dominants at several sampling stations in this

sector. One reason for this vegetation change may be that this upstream end of

the Lake is close to sources of propagules inflowing from the Sudanese River

Nile. The somewhat higher species diversity of sites at this end of the Lake (a

mean of 3.6 taxa per station, compared with 2.7 for Lake Nasser as a whole)

may be related to this factor. Springuel & Murphy (1991) emphasised that

further studies are needed to further explain these observations as little is

known at present about origins of euhydrophyte populations which have

succeeded in colonising Lake Nasser.

In 1984-1986, Ali (1987) found 7 species: N. marina subsp. armata, N.

horrida, Potamogeton crispus, P. pectinatus, P. trichoides, Vallisneria spiralis and

Zannichellia palustris. In 1986, Najas marina subsp. armata, N. horrida, Potamogeton

crispus, P. trichoides, V. spiralis and Z. palustris were recorded (Springuel 1987).

In 1988-1990, Ali et al. (1995) recorded 6 species: N. horrida, N. marina subsp.

armata, Potamogeton lucens, V. spiralis, Zannichellia palustris and Nitella hyalina

(Table 39). The latter species was misidentified in the previous work as Chara

sp. by Abdin (1949a) and Entz (1980b). Lake Nasser has shown a decrease in the

number of species present, especially those which are not tolerant to extreme

fluctuations in water level, Ceratophyllum demersum is one species that, although

present downstream of the Dam, has never been recorded in Lake Nasser either

before or after the Dam construction.

Subsequent to the construction of the Aswan High Dam, two

euhydrophytes disappeared from the region (Alisma gramineum Lejeune and

Damasonium alisma Mill. var. compactum (CAI). However, it seems that another

four species have colonized the Lake, with varying degrees of success (Table

39). The current dominants are the macrophyte flora Najas spp. and these

species which occurred in Nubian waters pre- 1964. Potamogeton crispus and P.

pectinatus are common species in the River Nile and Aswan Reservoir, but now

appear to be absent from Lake Nasser (Ali 1992). Zannichellia palustris remains

confined to the area of the Nile Valley now filled by Lake Nasser, but Vallisneria

spiralis is a fairly common plant in water bodies throughout Egyptian Nubia

(Belal et al. 1992).

The construction of the Aswan high Dam, with the subsequent creation

of new modified aquatic habitats for macrophyte growth in Egyptian Nubia,

had a profound effect on the aquatic flora of the region. Although Lower Egypt

probably retains, at present, its status as the more important area for aquatic

plant growth, there is now a strong evidence for the existence of trends of

increasing diversity and abundance of the freshwater macrophyte flora in

Upper Egypt. (Belal et al. 1992).

8

Ta

ble

39

Fre

shw

ate

r su

bm

erg

ed

macr

op

hy

tes

(flo

weri

ng

an

d n

on

-flo

weri

ng

) sp

eci

es

reco

rded

in

Eg

yp

tian

Nu

bia

pre

- an

d p

ost

- co

mp

leti

on

of

the A

swan

Hig

h D

am

(1962

-1993).

[Pla

tes

1-5

]

Ali

(1

99

8)

Per

son

al

com

mu

nic

ati

on

- - + - - - + - +

+ - +

+ - +

+

* =

no

t re

cord

ed

**

abse

nt

by

198

6

Ali

(1

99

2)

1989

-91

- - + - - - + - +

+ - +

+ - + -

Ali

(1

98

7)

1984

-86

- - +

+ - + - - +

+ - +

+ - - -

Sp

rin

gu

el

&

Mu

rph

y (

19

91

)

1980

-86

- - +

+ - + -

+

**

+

+

+

+

+

+ - -

En

tz

(19

76

)

1972

-74

- - - + - - - - - + - - +

+ - -

Ab

da

lla

h e

t a

l.

(1972)

1962

-64

-* - +

+

+ - - - + - - - - - - -

El-

Ha

did

i

(19

76

)

1963

-64

+

+

+

+

+ - - - +

+ - - + - - -

Bo

ulo

s

(19

66

)

1963

-64

+

+

+

+

+ - - - + - - - - - - -

Sp

eci

es

Ali

sma

gra

min

eum

Da

ma

son

ium

ali

sma

Po

tam

oge

ton

cri

spu

s

Po

tam

oge

ton

pec

tin

atu

s

Po

tam

oge

ton

per

foli

atu

s

Po

tam

oge

ton

tri

cho

ides

Po

tam

oge

ton

lu

cen

s

Po

tam

oge

ton

no

do

sus

Za

nn

ich

elli

a p

alu

stri

s

Va

llis

ner

ia s

pir

ali

s

Na

jas

min

or

Na

jas

ho

rrid

a

Na

jas

ma

rin

a

sub

sp.a

rma

ta.

Ch

ara

sp

. (m

isid

en

tifi

cati

on

)

Nit

ella

hy

ali

na

(m

acr

oa

lga

)

My

rio

ph

yll

um

sp

ica

tum

9

Succession of macrophyte species and community distribution in Lake Nasser (1988-1990)

Studies on Lake Nasser showed that it is a fairly hard-water, eutrophic

lake. It seems that several of the euhydrophyte species present are associated

with eutrophic conditions, including Zannichellia palustris, and P. crispus.

Others, including Vallisneria spiralis and Najas spp., may be less well adapted to

survival in the productive environment of Lake Nasser, where competition-

tolerance strategy traits will be an advantage (Springuel & Murphy 1991).

Springuel & Murphy (1991) studied the seasonal growth and distribution

of euhydrophytes in Lake Nasser and River Nile, and pointed out that Najas

horrida, N. armata and Potamogeton pectinatus displayed a spring/summer

decline in abundance with autumn and winter peaks of production.

Furthermore the depth distribution in the Lake showed differential colonisation

of different zones by individual species. The shallow zone in the Lake (0-0.5 m)

was preferentially occupied by Zannichellia palustris, in the areas where this

species was present (approximately 27% of the Lake shoreline). The less

common Potamogeton pectinatus and P. trichoides occurred preferentially at

intermediate depths (0.51-1.00 m). However, these species also occurred within

this zone with P. trichoides penetrating, at a few sites, as deep as 1.5 m. The

remaining species which include the principal dominants of the Lake

macrophyte community, occur in all depths from the surface to 3.00 m. No

species preferentially occurred in water deeper than 1.00 m in Lake Nasser.

Records of the euhydrophytes at 16 sites along the Lake (Fig. 66 and Table 40) between 1988 and 1990 indicated the dominance of Najas marina subsp. armata and Najas horrida. Potamogeton lucens, found in Lake Nasser only at Kalabsha, was previously incorrectly identified as P. nodosus (Springuel 1985b, Springuel & Murphy 1991).

Effect of water level on aquatic macrophytes of Lake Nasser

Habitat disturbance appears to be an important factor influencing the

macrophytes of Lake Nasser with the fluctuations of the water level being the

most important factor. Springuel et al. (1991) carried out a comparative study on

the species composition and growth of aquatic macrophytes in Lake Nasser,

Aswan Reservoir and the River Nile itself, downstream of the old Dam, as they

have major differences in physical conditions, notably in water level and

fluctuation regime. In Lake Nasser there is an annual cycle of water level

change related to the seasonal flood pattern of the River Nile. In Aswan

Reservoir, mean monthly water levels are relatively constant, although there is

a diurnal range of about 3 m related to the daily pattern of inflow through the

High Dam turbines.

11

Ta

ble

40

Dry

wei

gh

t st

and

ing

cro

p (

g/m

2 ) o

f eu

hy

dro

ph

yte

s in

sh

allo

w a

nd

dee

p w

ater

zo

nes

du

rin

g 1

989

at 1

6 si

tes

in L

ake

Nas

ser

at v

ario

us

sam

pli

ng

tim

es (

Ali

199

2). [

Fo

r lo

cali

ties

ref

er t

o F

ig. 6

6].

Tu

rgu

mi

3 M

ar.

- - -

31

.59

1

- - - -

*(-)

=n

ot

reco

rde

d

10

Oct

.

- - -

7.1

92

- - - -

1 Ja

n.

16

.36

- -

13

.46

- - - -

4 A

pri

l

4.2

88

- -

1.0

- - - -

El-

Mad

iq

6 S

ept.

-

0.0

05

-

0.3

31

0.0

45

-

0.8

03

-

Kal

absh

a

(a)

6 S

ept.

- - -

0.0

4

4.5

63

- - -

Ab

u H

or

11 F

eb.

0.4

9

-

0.0

27

0.8

1

- - - -

12 F

eb.

0.2

-

0.0

05

2.8

01

-

0.3

73

-

Am

ada

7 S

ept.

- - - -

0.9

63

-

5.4

23

Mir

waw

Eas

t

14 F

eb.

-

10

.86

0.2

9

3.9

4

- - - -

Mir

waw

Wes

t

14 F

eb.

-

1.1

27

0.3

4

1.1

71

-

0.1

99

- -

El-

Bir

ba

Eas

t

2 O

ct.

- - -

0.0

11

28

.11

- - -

11 M

ay

- - -

El-

Bir

ba

Wes

t

11 M

ay

3.2

42

- -

12

.53

4.4

1

- - -

Kal

absh

a

(b)

1 O

ct.

- - -

16

.26

3

0.0

94

-

0.0

08

3.8

99

Mar

iya

17 F

eb.

0.1

14

-

0.2

52

3.5

1

- - - -

So

lim

an

16 F

eb.

0.4

-*

-

1.5

5

- - - -

Zo

nes

& S

pec

ies

Sh

allo

w Z

on

e

N.

ma

rin

a

N.

ho

rrid

a

Z.

pa

lust

ris

Dee

p Z

on

e

N.

ma

rin

a

N.

ho

rrid

a

Z.

pa

lust

ris

V.

spir

ali

s

P.

luce

ns

11

Fig. 66 Outline map of Lake Nasser showing sampling sites () and selected

sites used (▲), 1: El-Birba West, 2: El-Birba East, 3: Abisco, 4: Abu Hor, 5:

Kalabsha (a), 6:Kalabsha (b), 7:Mirwaw East, 8:Mirwaw West, 9: Soliman,

10:Mariya, 11:Turgumi, 12: Allaqi, 13:Kourta II, 14:Amada, 15:El-Madiq,

16:Adindan (Ali 1992).

There were major differences in community dominance between the three systems. Najas marina subsp. armata dominated the highly disturbed littoral zone of Lake Nasser, making up nearly 40% of the total standing crop. Other species present were Najas horrida, Vallisneria spiralis and Charophyta. However, in both Aswan Reservoir and River Nile, the dominant species were Ceratophyllum demersum (comprising 59-78% of total standing crop) and Potamogeton crispus (15-20% of total crop). In terms of relative standing crop

12

these species virtually excluded all others from the reservoir, but in the river approximately 25% of the total submerged standing crop was made up of other species, notably Potamogeton perfoliatus and Myriophyllum spicatum. It is suggested that the High Dam represents a major vegetation boundary in the River Nile ecosystem.

Ali et al. (1995) found that peak growth in the shallow water zone tended

to occur following inundation or reinundation of sites by rising water levels,

following exposure of sites. This produced a discontinuous distribution, over

the time, of short established-phase submerged macrophytes, with a long

period when no plants are present. In contrast macrophytes are always present

in the deeper zone. There are geographical differences in distribution. Najas

horrida was dominant in the northern section of the Lake (El-Birba - Fig. 66).

Further south, Najas marina dominated the aquatic community at Turgumi and

Kalabsha (in the middle section of Lake Nasser). At the southernmost site,

Amada (west bank) Najas spp. were largely replaced by Vallisneria spiralis, as a

dominant species, occurring at the only site with a fine sand hydrosoil. In May

1989 N. marina subsp. armata became more abundant and reached its highest

biomass of 507.44 g/m2 (Table 41).

Table 41 Dry biomass (g/m2) of euhydrophytes and macroalgae in the shallow water zone at Turgumi, Lake Nasser (Ali 1992).

Species April 1989 May 1989 July 1989 May 1990

Najas marina 114.87 507.44 120.94 47.93

Najas horrida --- --- --- 50.37

Nitella hyalina 103.12 54.30 --- 37.55

Zanichellia palustris --- --- --- 1.25

ALGAE

PHYTOPLANKTON

The formation of Lake Nasser was accompanied by structural and

physico-chemical changes which consequently affected the river biota. These

changes lead to corresponding qualitative and quantitative alterations in the

composition of the phytoplankton community.

Species Diversity The community of planktonic algae in Lake Nasser is fairly diverse,

belonging mainly to four divisions: Chlorophyta, Bacillariophyta, Cyanophyta

and Pyrrophyta. Samaan (1971) recorded 27 species, while Latif (1974b)

mentioned only 20 species. Zaghloul (1985) recorded 43 species, while

Mohamed, et al. (1989) recorded 50 species belonging to the four divisions

(Table 42).

13

Table 42 Inventory of phytoplankton species recorded from Lake Nasser from

1981 to 1993. [PLATES 6-12]

Taxa & Species 1981

Zaghloul

(1985)

1982/84

Mohammed,

et al (1989)

1993

Abdel-Monem

(1995)

CHLOROPHYCEAE Palmellaceae

Asterococcus limneticus (Cienkowski) Scherffel

Chlamydocapsa planctonica W. & G.S.West

(=Gloeocystis planctonica G.gigass Kütz. Lage)

-

-

-

+

+

+

Coelastraceae

Chlorococcum aegyptiacum Archibald

(=Cholorella Beijerinck)

Coelastrum microsporum (Nägeli) var. microsporum

(=C. robustum Haz. 1964, Chlorella regularis Oltm 1904)

C. reticulatum (Dangeard) seen var.

reticulatum

(= C. distans Turn. 1982)

-

-

-

-

+

-

+

+

+

Desmidiaceae

Cosmarium contractum (Kirchner)

C. depressum Lundell

C. subtumidum Nadst.

Staurastrum paradoxum Meyen

S. tetracerum Ralfs

S. uniseriatum Nyg.

Closterium venus Kütz.

-

-

+

+

-

-

-

-

+

-

-

-

+

+

+

-

-

+

+

-

-

Dictyosphaeriaceae

Dictyosphaerium elegans Bachmann

D. ehrenbergianum Nägeli

D. pulchellum Wood

D. subsalitarium Van Goor

(=Dictyosphaerium primarium = D. simplex Skuja)

-

-

+

-

-

-

+

-

+

+

+

+

Micractinaceae

Golenkinia radiata Chodat

-

+

+ Oocystaceae

Ankistrodesmus falcatus (Corda) Ralfs

A. fusiformis Corda

Lagerheimia citriformis (Snow) G.M.Smith

(=Chodatella citriformis Snow)

L. ciliata (Lager.) Chodat.

(= Chodatella ciliata Lagerh. Lemm.)

L. longiseta (Lemm.) Wille

(=Chodatella longiseta Lemm.)

L. quadriseta (Lemm.) G.M. Smith

+ - - - - -

+ - -

+ - -

+ + +

+

+

+

14

(=Chodatella quadriseta Lemm.)

L. subsalsa Lemm.

(=Chodatella susbsalsa Lemm.)

Monoraphidium minutum (Nägeli) Komm. Leg.

( = Selenastrum minutum Nag. Collins)

M. contortum (Thuret) Komm.

(=Ankistrodesmus falcatus var. duplex Kütz.

=A. f. var spirilformis G.S. West)

M. convolutum (Cord) Komm.

(=Ankistrodesmus convulutus Corda)

M. griffithii Berk. Komm.

(=Ankistrodesmus acicularis A. Braun.

Korsh. = A. f. var acicularis Braun)

- - - - -

- - - - -

+

+

+

+

+

M. komarkovae Nygaard

(=Ankistrodesmus facatus. var setiformis Nyg.)

Oocystis sp.

Oocystis lacustris Chodat

O. borgei Snow

O. elliptica W. West

O. parva W. & G. S. West

Closteriopsis longissima Lemm.

Franceia sp.

Kirchneriella microscopica Nyg.

Tetraedron minimum (A. Br.) Hansg.

-

+ - - - - - - - -

- - - + - - + + + +

+ - + + + + + - - -

Hydrodictyaceae Pediastrum duplex Meyen

Pediastrum duplex var. gracillium W. & G. S. West

P. simplex Meyen

(= P. clathratum Sch. Lemm.)

P. simplex var. biwaense Fukush.

P. simplex var. radians Lemm.

P. boryanum (Turipn) Menegh.

Planktosphaeria gelatinosa G.M.Smith

- - + - + + -

+ - + - - - -

- + +

+ - - +

Characiaceae Schroederia setigera (Schroed.) Lemm.

-

+

-

Scenedesmaceae Crucigenia quadrata Morren

Scenedesmus arcuatus Lemm.

S. bijugatus (Turp.) Kütz.

S. diamorphus Turp.

S. quadricauda (Turp.) Brèb.

S. obliquus (Turp.) Kütz.

Actinastrum hantzschii Lagerh

- - + + + - +

+ + - - + + -

- - - - - - -

Zygnemataceae Spirogyra Link.

+

-

-

-- - - + + -

+ + - + +

+ - + - -

Chroococcaceae Chroococcus minutus (Kütz.) Näegeli - - +

15

C. dispersus (Keissler) Lemmermann + - + C. limnetica Lemm. - + + C. turgidus (Kütz.) Nägeli - - + Dactylococcopsis sp. - + - D. acicularis Lemm. + - - Gomphosphaeria lacustris Chodat + + +

(=G. littoralis Hayren) G. lacustris var. compacta Lemm. - - +

(= G. compacta Lemm.Strom.) Merismopedia warmingiana Legerheim - - +

(=M. tenuissima Lemm.) M. minima Beck. - - + M. punctata Meyen. + - + M. tenuissima Lemm. - + - Microcystis aeruginosa Kütz + - +

(= M. flos-aquae Witt. Kir.) M. wesenbergii (Komarek) Starmach - + - M. elachista W. & G. S. West Starmach + - +

(=Aphanocapsa elachista W. & G. S. West) M. grevillei Hassal Elenkin - - +

(=Aphanocapsa gravillii Hass Kabenhorst) M. rainbaldii Richter Forti - - +

(=M. holsatica Lemm. = M. pulverea Wood Forti = M. p. var. incerta Lemm. Crow = Aphanocapsa delicatissima W. & G. S. West) Oscillatoriaceae

Lyngbya limnetica Lemm. + + + Lyngbya sp. - - + Oscillatoria limnetica Lemm. + - + O. planctonica Wolosz. + - + Oscillatoria. sp. - + + Phormidium africanum Lemm. - - + P. mucicola Naum. & Huber. - - + P. tenue (Menegh.) Gom. - - + P. corium (Ag. ) Gom. - - + Phormidium sp. - + - Spirulina laxissima G.S. West + - - Spirulina sp. - + - BACILLARIOPHYCEAE

Coscinodiscinaceae Aulacoseria muzzanensis Meister Krammer - - +

(=Melosira muzzanensis Meister = M. granulata var muzzanensis Bethge)

A. granulata Ehre. Simonsen. + - + (=M. granulata (Ehr.) Ralf = M. lineolata Gru.)

A. g. var. angustissima O. Müller Simonsen + - + (=M. g. var. angustissima O. Müller)

A granulata. var. valida Hust. - - + Cyclotella ocellatus Pantocsek - - + C. glomerata Bachmann - - + C. kützingiana Thwaites - + + C. meneghiniana Kütz. + + + Melosira agassizii Ostef var. malayensis Hust. - - +

16

M. nyassensis O. Müller - - + M. nyassensis var victoriae O. Müller - - - M. distans var. distans (Ehr.) - - + M. granulata (Ehrbg.) Ralfs + + - Stephanodiscus aegyptiacum Ehr. (S. nana Meister) - - +

Fragilariaceae Synedra ulna Ehrbg. + + + S. tabulata (Ag.) Kütz. + - -

Naviculaceae Diploneis sp. - + - Gyrosigma attenuatum (Kütz) Rabenh. - + - Navicula pupula Kütz. - + - N. radiosa Kütz. - + - Navicula sp. + + - Pleurosigma elongatum Sm. + - -

Achnanthineae Cocconeis placentula Ehrbg. + - -

Gomphonemataceae Gomphonema lanceolatum Ehrbg. - + - Amphora ovalis Kütz. + + -

Cymbellaceae Cymbella tumidae (Bréb) van Heurk + + - Epithemia sorex Kütz. - + - Epithemia gibbrula Ehrbg. + - - Rhopalodia sp. - + -

Nitzschiaceae Nitzschia microcephala (Grun.) + - - N. palea (Kütz.) W. Sm. + - - N. apiculata Greg. + - -

Surirellaceae Surirella ovalis Bréb. + - -

DINOPHYCEAE (PYRRHOPHYTA) Ceratiaceae

Ceratium furcoides (Levander) Langhans - - + (= C. hirudinella var. furcoides Levander)

C. hirundinella Bergh. + + + C. cornutum (Ehr.) - - +

Gymnodiniaceae Gymnodinum lantzchii Ütermöhl. - - +

Peridiniaceae Peridinium africanum Lemm. Lif. - - +

(=P. intermedium Thompson = P. cinctum O.F. Müller) P. inconspicüm Lemm. F. Armatum - - + P. pigmeum (Lin.) Baurrelly - - + P. wierejskii Woloszynska - - + P. willei Huitfeld-Kass - - + Peridinium. sp. - + - Peridiniopsis pygmaium (Lin.) Bourrelly - - +

Glenodiniaceae Glenodinium sp. + - -

EUGLENOPHYCEAE Euglena acus Ehr. + - -

17

Note: Mohamed, I. (1993g) recorded also the genus Microcystis sp. (Cyanophyceae).

In 1993 Abdel-Monem (1995) recorded 84 planktonic algal species

including 35, 23, 15 and 11 species of Cyanophyceae, Chlorophyceae,

Bacillariophyceae and Dinophyceae, most of these were not recorded by

previous investigators (Table 42). Although the number of species is high, only

a limited number formed the main bulk of phytoplankton communities. Green

algae contributed more genera to the phytoplankton than any other group.

However, diatoms and blue-green algae were found to be alternatively the

dominant groups. These two dominant groups exhibited seasonal, local and

vertical variations along the main body of the Lake.

The total number of phytoplankton species recorded from Lake Nasser

during the period 1981-1993 (Table 42) is 135 species belonging to five classes:

54 spp. of Chlorophyceae, 34 spp. of Cyanophyceae, 33 spp. of

Bacillariophyceae, 13 spp. of Dinophyceae and 1 sp. of Euglenophyceae.

The components of the plankton community are comparable to those

in the White Nile between Khartoum and Gebel Aulia Dam (Brook & Rzóska

1954, Talling 1957a, Abu-Gideiri 1969, Talling 1976b), the Blue Nile (Talling &

Rzóska 1967), some Central East African waters such as Lake Kyoga (Evans

1962), Lake Victoria (Talling 1957b and 1976b) and Lake Belwood

(Duthie 1968).

Phytoplankton Standing Crop

The phytoplankton community in Lake Nasser is rich both in numerical density and biomass.

Density. Numerically, Bacillariophyceae and Cyanophyceae are the main

components, while Dinophyceae, Chlorophyceae and Euglenophyceae

persisted as frequent or rare forms. Thus, in 1993 Abdel-Monem (1995) found

that the annual averages of Cyanophyceae ranged from a maximum of 83.7%

forming a major peak in autumn and a minimum of 21.8 %, in winter.

Following the Cyanophyceae, Bacillariophyceae constituted 76.7 % of the total

crop in winter, and a minimum (13.3 %) in autumn. Chlorophyceae occupied

the third predominant group with population densities ranging from 20.6 % in

spring to a minimum of 2.1 % in winter. Dinophyceae being the least

represented in number of species and density, they ranged from 1.4 % in spring

to nil in winter.

Samaan & Gaber (1977) mentioned that because the flood-affected

regions of the Lake exhibit different characteristics from the areas beyond the

reach of the flood, the phytoplankton was different in terms of number and

types at different periods of the year. Gaber (1982) pointed out that in October

18

1979 Cyanophyceae constituted 81.23 % of the total phytoplankton community

(average 2.52x106 algal units/l), while Bacillariophyceae formed 13.86% by

number (average 0.43x106 algal units/l). The percentage of Cyanophyceae

increased from the High Dam to Amada (91.72 %), and reached its maximum

value (95.57 %) in Khor Singari. Then it decreased gradually from Tushka to

Adindan where it reached 31.05%. The average number of diatoms remained

low between the High Dam and Amada, but showed a rapid increase from

Tushka to Adindan (Gaber 1982). Chlorophyceae in the Lake remained low, as

they constituted only about 4.9 % by number of the total phytoplankton

(average 0.152x106 units/l). Generally, Chlorophyceae were concentrated in the

northern part of the Lake. The highest percentage was observed in Khor

Kalabsha and decreased in the southern part and reached the least percentage

in Tushka (0.054x106 algal units/l) and in Khor Or (0.016x106 algal units/l)

(Gaber 1982). The Dinophyceae were rarely represented in the Lake by

Peridinium sp. and in average numbers of 500 unit/l, contributing only about

0.01% of the total community (Gaber 1982).

Latif (1984b) showed that in March and August 1976, the phytoplankton

in Lake Nasser, was in the range of 3.2 to 11.5 x106 algal units/l and 4.7 to

9.5x106 algal units/l respectively (Fig. 67). Variations in the number and

percentage of phytoplankton at different stations along the main channel of

Lake Nasser (1976) show that the northern 100 km had a higher number of

phytoplankton in August than in March (Latif, 1984b -Fig. 67). At the same

time, the central part of Lake Nasser, extending from El-Madiq to Amada, did

not show great changes in the number of phytoplankton cells. The region from

Tushka to Adindan showed the widest difference. The latter author pointed out

that during flood time (August) flood waters push ahead great amounts of

phytoplankton to the northern part of the Lake, thus resulting in the highest

figures recorded throughout the year. Nevertheless, due to riverine conditions,

Adindan presented lower values in August than in March.

Latif (1984b) pointed out that in August 1976, cyanophytes were the

most common, as their percentage ranged from 87.4 to 96.4% (average 94.3%);

while diatoms formed only 2.7% (range 1.1 to 9.0%). From the High Dam to

Amada, cyanophytes were more common than diatoms and their percentage

varied from 71.2 to 89.0%. However, at Tushka and Adindan, cyanophytes

comprised a very small percentage, i.e. only 7.0 and 0.9%, respectively, and in

contrast diatoms constituted the major part of phytoplankton forming 92.3 and

98.6%, respectively (Latif 1984b). Chlorophytes did not show wide differences

and were of low magnitude, i.e. 0.5 to 3.0% of the total numbers in March, and

2.2 to 3.6% in August. Thus, in the post-flood season, diatoms form the most

common phytoplankton in the areas affected by the flood (Fig. 67-Latif 1984b).

19

Based on the observations of Zaghloul (1985) and Abdel-Monem (1995)

the specific variations of phytoplankton in Lake Nasser may be summarized as

follows:

1- The standing crop of phytoplankton tended to increase southwards from

3.405x106 algal units/l at El-Birba to 15.272x 106 algal units/l at Adindan.

2- The density of the phytoplankton standing crop was 6.258x106 algal units/l

in the surface water. This value decreased to 2.08x106 algal units/l at 20 m

depth (Zaghloul 1985). These values coincide with those obtained in 1993 by

Abdel-Monem (1995) who showed that the average seasonal annual density at

subsurface waters was of 1.017x106 and 0.918 x106 algal units/l at 15m depth

and 0.984 x106 near the bottom at 6 sites in the main channel. It seems that the

difference in density in different years may be attributed to the limited number

of samples collected at different localities.

3- Bacillariophyceae contributed 50.06% by number to the total phytoplankton.

They were represented mainly by Melosira sp., which constituted numerically

over 99% of the total diatoms. Other genera of frequent distribution included

Synedra and Nitzschia spp. Seven species were of rare occurrence (Zaghloul

1985). Abdel-Monem (1995), however, pointed out that diatoms in the main

channel were mainly represented by Aulacoseria granulata, Aulacoseria granulata

var. angustissima, Melosira nyassensis var. victoriae and Cyclotella ocellatus. Other

species of infrequent occurrence were: Aulacoseria muzzanensis, Melosira agassizii,

Cyclotella meneghiniana and C. glomerata. Most of these species were not recorded

by earlier authors.

4- The seasonal variations of Bacillariophyceae varied between the northern

and southern sectors as well as in the khors. Generally, their maximum

frequency was recorded in the southern region of the Lake in summer.

5- Cyanophyceae contributed numerically 47.45% of the total phytoplankton,

with annual averages of 3.146x106 algal units/l in the surface water and

0.813x106 algal units/l at 20 m depth. Anabaenopsis was the dominant genus

constituting about 93.41% of the total cyanophytes. Other genera with frequent

occurrence comprised Dactylococcopsis, Microcystis and Merismopedia spp. In

1993 the main species recorded by Abdel-Monem (1995) were Microcystis

aeruginosa, Chroococcus limnetica, Lyngbya limnetica, Oscillatoria limnetica and

Phormidium africanum. The less abundant species were Chroococcus minutus,

Merismopedia punctata, Microcystis grevillei, Oscillatoria planctonica and

Phormidium tenue.

Glenodinium sp. was the main representative of Dinophyceae. Its main

occurrence was confined to Khor Kalabsha in spring. Abdel-Monem (1995)

reported that Dinophyceae were very rare in 1993 and contributed about

21

0.6x104 algal units/l representing 1.08% of the total phytoplankton crop. Their

maximum occurrence was recorded in spring and summer while they were not

recorded in winter.

Fig. 67 Phytoplankton at different stations along the main channel of Lake Nasser in March and August 1976. A: number of phytoplankton (10

6/l), B:

percentage of Cyanophyceae and Bacillariophyceae (Latif 1984a).

7- Chlorophyceae contributed 0.43% of the total phytoplankton crop in the Lake

and consisted mainly of Pediastrum and Staurastrum spp. In 1993 Abdel-Monem

(1995) showed that green algae formed numerically about 6.4x104 algal units/l

representing 7.88% of the total phytoplankton crop. Their highest density was

recorded in spring (16.9x104 algal units/l, 20% of the total count), and the

lowest density in winter (1.9x104 algal units/l, 2.1% of total count).

Mohamed, I. (1993j) investigated the seasonal changes of vertical

distribution of phytoplankton in the main channel of Lake Nasser and found

that diatoms of genus Melosira contribute the highest number of cells in

February, May, August and November 1990 (Fig. 69). This agrees with the

observations of Zaghloul (1985).

Habib (1992b) found that in Khor El Ramla, the highest number of

phytoplankton cells was recorded in August 1988 (5.13x104 units/l) and the

lowest (0.32x104 units/l) in November 1986. Generally, all the stations in Khor

El Ramla showed a slow increase from February to September and November

(Fig. 72).

21

Biomass. Zaghloul (1985) summarized the biomass of phytoplankton collected

from Lake Nasser as follows:

1- The phytoplankton biomass reached annual averages of 22.913 and 4.088 mg/l in the surface water and at 20 m depth, respectively. Results indicate that the biomasses of the different phytoplankton divisions were altered when compared with their numerical distribution.

2- The phytoplankton biomass increases southwards to the highest value of 45.065 mg/l at Adindan due to the increased numbers of Chlorophyceae and Bacillariophyceae. It showed also a different seasonal periodicity within the northern and southern sectors and khors, but reached its peak at most stations in spring and also at Adindan in winter.

3- Although numerous species were recorded in the Lake, yet few of them formed the main bulk of phytoplankton biomass with a specific distribution at the different localities. Thus, Glenodinium sp. was confined to Khor Kalabsha where it formed 95% of the total phytoplankton by weight . On the other hand, Melosira granulata and Pediastrum spp. were the main biomass components at Adindan.

Horizontal, vertical and seasonal distribution

The horizontal distribution of the total phytoplankton in the upper 10 m showed a marked increase from the High Dam (average 2.708x106 algal units/l) to Kalabsha (average 3.440x106 algal units/l). A slight drop was recorded at Allaqi (average 2.994x106 algal units/l) (Table 43 and Fig. 68 - Gaber, 1982). Another gradual increase was recorded at El-Madiq, and this was succeeded by a rapid decrease in the total number of phytoplankton southwards, reaching the lowest value at Adindan (0.948x106 algal units/l). In 1993, Abdel-Monem (1995) studied the horizontal, vertical and seasonal variations of the phytoplankton standing crop in the main channel and found that the highest seasonal average was attained in winter (1.327x106 algal units/l), followed by autumn (1.085x106 algal units/l) and spring (0.93x 106 algal units/l). The lowest average value was recorded in summer being 0.729x 106 algal units/l. The maximum standing crop (5.92x 106algal units/l) was recorded at Dihmit near the bottom, while the lowest was found in summer (4x 106 algal units/l) near the bottom at Tushka.

Khors sustained higher density of phytoplankton than the main stream; their numbers increased to 3.622x106 algal units/l at Khor Kalabsha and 5.234x106 algal units/l at Khor Singari (Table 43 and Fig. 68 - Gaber 1982).

Gaber (1982) recorded the vertical distribution of the total phytoplankton at the different stations in October 1979 as shown in Table 43. It appears that the phytoplankton profile remained, more or less, constant at the northern section of the Lake i.e. from High Dam to Kalabsha. The distribution of phytoplankton at Amada showed relatively higher values at 3 m depth, mainly due to

22

Cyanophyceae. The number of phytoplankton at El-Madiq and Abu Simbel showed higher values at the surface when compared with that of the subsurface water. The maximum distribution of phytoplankton was recorded in Khor Singari at 1 m depth being 7.62x106 algal units/l (Gaber 1982 - Table 44).

Mohamed, I (1993j) carried out studies on the seasonal, vertical and

horizontal distribution of the dominant phytoplankton species in the main

channel of Lake Nasser (Figs. 69 and 70) at six stations. It was obvious that the

highest number of diatoms (mainly Melosira sp.) was found during February

and May 1990. In February 1990, Melosira spp. contributed the highest number

of cells at all stations (Fig. 69), followed by Oscillatoria sp. (Cyanophyta) (Fig.

70), while Navicula spp. (Bacillariophyta) were found in the lowest number of

cells and was recorded only at station 1 at depths 5, 10, 15 m (Fig. 70).

Staurastrum sp. and Ankistrodesmus spp. (Chlorophyta) appeared at stations 2, 3

and 4 for both genera, and stations 5 and 6 for Staurastrum sp. (Fig. 70).

23

Fig. 68 Distribution of phytoplankton density in Lake Nasser in October 1979

(Gaber 1982).

24

Ta

ble

43

Dis

trib

uti

on

o

f th

e

dif

fere

nt

gro

up

s o

f p

hy

top

lan

kto

n (1

06u

nit

/l)

in L

ak

e

Nass

er

an

d

their

perc

en

tag

e d

en

sity

to

to

tal

po

pu

lati

on

du

rin

g O

cto

ber

1979 (

Gab

er

1982).

Sit

e

Cy

an

op

hy

cea

e

Ch

loro

ph

yce

ae

B

aci

lla

rio

ph

yce

ae

D

ino

ph

yce

ae

To

tal

N

o.

%

No

.

%

No

.

%

No

.

%

Hig

h D

am

2

.19

2

80

.95

0

.22

2

8.3

3

0.2

94

1

0.8

6

---*

--

-

2

.70

8

Kala

bsh

a

2.8

78

8

3.6

6

0.3

12

9

.07

0

.24

4

7.0

9

0.0

06

0

.17

3

.44

0

Kh

or

Kala

bsh

a

3.0

08

8

3.0

5

0.3

28

9

.06

0

.28

6

7.9

0

---

---

3.6

22

All

aq

i 2

.55

8

85

.44

0

.24

2

8.0

8

0.1

94

6

.48

--

- --

-

2

.99

4

El-

Ma

diq

3

.87

2

90

.84

0

.22

8

5.4

0

0.1

60

3

.76

--

- --

-

4

.26

0

Kh

or

Sin

gari

5

.00

2

95

.57

0

.10

0

2.1

0

0.1

22

2

.33

--

- --

-

5

.23

4

Am

ad

a

3.3

68

9

1.7

2

0.1

44

3

.92

0

.16

0

4.3

6

---

---

3.6

72

Tu

shk

a

1.7

16

6

2.6

7

0.0

54

1

.97

0

.96

8

35

.35

--

- --

-

2

.73

8

Kh

or

Tu

shk

a

4.4

04

7

4.5

0

0.0

78

2

.47

0

.74

6

23

.08

--

- --

-

3

.23

2

Ab

u S

imb

el

2.1

48

6

7.8

4

0.0

92

2

.91

0

.92

6

29

.25

--

- --

-

3

.16

6

Kh

or

Or

0.6

52

5

1.3

4

0.0

16

1

.26

0

.60

2

47

.40

--

- --

-

1

.27

0

Ad

ind

an

0

.48

4

51

.05

--

- --

- 0

.46

4

48

.95

--

--

0

.94

8

Av

era

ge

2

.52

3

81

.23

0

.15

2

4.9

0

0.4

30

1

3.8

6

50

0/

l 0

.01

3.1

07

*

(--

) n

ot

reco

rded

.

25

In May 1990, Melosira sp. was recorded with the highest number of cells

(Fig. 69). Microcystis sp. (Cyanophyta), Cyclotella sp. (Bacillariophyta) (Fig. 69)

were represented by a high number of cells; while Coelastrum, Staurastrum and

Merismopedia spp. (Figs. 69 and 70), Peridinium sp. and Ceratium sp. (Fig. 70)

were recorded in the lowest number.

In August 1990, Melosira sp. was found in the highest number of cells and

appeared at all stations except station 4 (Fig. 69). Microcystis sp. was recorded in

all stations (Fig. 69) and Scenedesmus sp. only in station 1 (Fig. 70) and were

present in high number of cells.

In November 1990, Melosira spp. and Microcystis spp. were recorded with the highest number of cells at all stations except station 1 (Fig. 69), while Coelastrum sp. was observed in high number (Fig. 70). The other genera except Pediastrum were found in lower number of cells (Figs. 69 and 70).

It is worth mentioning that phytoplankton in Lake Nasser revealed

vertical variations during the periods of thermal stratification (late spring,

summer and early autumn months). Diatoms and blue-green algae

(Cyanobacteria) remained the dominant groups also in the lower layers.

Moreover, Cyclotella sp. and Anabaenopsis spp. were the dominant genera in

diatoms and blue-greens. Habib (1998a) pointed out that the percentage

composition of blue-greens in 1991 dominated the community during spring

and summer, being more tolerant to relatively high temperatures. Diatoms

dominated the community once in winter (December).

Although oxygen concentration was always under the saturation level, the phytoplankton abundance in spring and summer was accompanied by high oxygen saturation levels, pH values and chlorophyll a concentrations (Belal et al. 1992). The latter authors found that the temporal course of algal development showed, more or less, the opposite trend to that of the dissolved nitrate-nitrogen (Table 45). Variations in time of the nitrate-nitrogen concentration, chlorophyll a and total phytoplankton populations are presented in Fig. 71.

Habib (1995c) in her investigation on the seasonal variation of phytoplankton at four stations in Khor El Ramla from September 1986 to December 1988 recorded three peaks in the total number of the population in November 1986, November 1987 and August 1988 (Fig. 72). The highest peak was recorded in August 1988 ( 5.13x104 algal units/l), and the lowest (0.32x104 algal units/l) in November 1986. Generally, all the stations showed a slow increase from February to September and November 1987 recording a second peak. The four stations showed the same trend of seasonal variation, recording a gradual decrease through autumn and winter. Generally, chlorophyll a peak always preceded or coincided with the peak of plankton numbers.

26

Fig. 69 Seasonal changes of vertical distribution of phytoplankton in the main channel

in 1990 (Mohamed, I. 1993j). Scale bar = 1000 cells/ml. [For stations refer to Fig. 4].

27

Table

44 V

erti

cal

dis

trib

uti

on

of

the

tota

l n

um

ber

of

ph

yto

pla

nk

ton

(10

6 a

lgal

un

its/

l) r

ecord

ed a

t d

iffe

ren

t st

ati

on

s d

uri

ng

Oct

ob

er 1

979 (

Gab

er 1

982).

10m

1.9

46

2.9

54

4.8

44

1.7

92

4.5

50

4.6

34

2.3

10

2.6

04

2.2

82

1.7

08

0.7

00

0.7

28

5m

2.6

04

3.0

06

2.8

84

3.0

94

3.9

62

3.3

74

3.0

24

2.3

52

3.5

70

3.1

08

0.8

82

1.1

34

4m

3.0

10

3.3

46

4.0

46

3.2

34

3.9

20

3.9

90

2.6

18

2.1

00

3.5

56

2.8

84

1.2

88

1.0

08

3m

2.8

28

3.4

16

3.3

74

2.8

84

4.9

20

4.8

84

4.9

70

2.3

38

3.3

74

3.3

60

1.3

72

1.1

20

2m

2.6

60

3.7

38

3.0

24

3.5

84

4.1

86

6.6

22

4.2

84

9.8

98

2.7

72

2.6

32

1.7

92

1.0

08

1m

2.9

54

3.0

24

3.5

98

3.4

30

3.8

08

7.6

02

4.4

10

3.6

54

4.6

90

3.0

38

2.0

44

9.9

80

Su

rface

2.9

45

4.5

36

3.5

84

2.9

40

5.0

26

6.1

32

4.0

88

3.2

20

2.3

80

5.4

32

0.8

12

0.6

58

Sit

e

Hig

h D

am

Kala

bsh

a

Kh

or

Kala

bsh

a

All

aq

i

El-

Mad

iq

Kh

or

Sin

gari

Am

ad

a

Tu

shk

a

Kh

or

Tu

shk

a

Ab

u S

imb

el

Kh

or

Or

Ad

ind

an

28

Fig. 70 Seasonal changes of vertical distribution of phytoplankton in the main channel in 1990 (Mohamed, I. 1993j). Scale bar = 1000 cells/ml. [For stations refer

to Fig. 4].

Needless to mention that phytoplankton in Lake Nasser, at present, diatoms and cyanophytes (Cyanobacteria) preponderate along the main channel and even at all sites because both groups are well adapted to the new environmental conditions. All phytoplankton groups are responsible for

29

primary production, which is the basis of food webs in Lake Nasser. Therefore, the phytoplankton could intensively influence the economy of such a man-made Lake. Hence, the recorded planktonic algae are considered as the major source of food for the plankton feeding fishes, which are the dominant species in the Lake.

WATER BLOOMS Sometimes serious problems of unbalanced biological conditions arise in

sluggish areas of Lake Nasser. Overgrowth of Cyanophyceae species causes floating crusts and scums, where plants die quickly and disintegrate in the intense sunlight. This causes depletion of oxygen below the point required for fish and other aquatic animals. Mohamed, I. (1993k) recorded the occurrence of water blooms in Lake Nasser eight times during six years (from 1987 to 1992) and pointed out that water blooms occurred only in very limited areas of the southern part of the Lake. Cyanophyceae species were found in all samples of blooms. Microcystis aeruginosa was the dominant species in all the samples of water blooms (Mohamed, I. 1993k) (Table 46). The latter author pointed out that Oscillatoria spp. were observed in extreme values at Korosko, while Aphanocapsa sp. was present in high quantities at Abu Simbel.

Recently, water blooms have been recorded in the central area of the Lake. Occassionally they were seen at Korosko in the northern area. Formerly M. aeruginosa water blooms occurred annually for several months before the flood water period, but now they may occur intermittently all the year round (Mohamed, I. & Ioriya, 1998).

Fig. 71 Depth-time distribution of NO3-N ; chlorophyll a concentration and of

total phytoplankton units under 1 m2 down to a depth of 3 and 20 m in the

Lake at site 1 (10 km south of AHD) [Mohamed et al. 1989].

31

Table 45 Temporal course of algal development and nitrate concentration by

representation of higher, middle, and lower values from March 1982 to February

1984. (Belal et al. 1992). 1982 1983 1984

M A M J J A S O N D J F M A M J J A S O N D J F

Total algal count -

Chlorophyll a

O2 (% Sat.)

pH --

NO3.N

maximum, moderate, minimum values, -- not measured.

Fig. 72 Seasonal variations of the total number of phytoplankton )algal units( at

Khor El Ramla at four stations (Habib 1995c) [For stations refer to Fig. 4].

CHLOROPHYLL a The amount of chlorophyll a in water is an index of phytoplankton

productivity and has been used to estimate the primary productivity in

combination with data on photosynthetic activity on chlorophyll a basis and

light conditions in freshwater lakes as well as in marine environments

(Ichimura et al. 1962, Aruga & Monsi 1963). It will be possible to calculate

primary productivity by phytoplankton in a lake on the basis of enough

information on the photosynthetic and respiratory activities of phytoplankton

and the diurnal and seasonal changes of light conditions.

31

Table 46 Cell number of water blooms in Lake Nasser (Mohamed, I. 1993k)

unit: cell/10 ml.

Genera

Date Site Micr. Nost. Anab. Osci. Phor. Melo. Apha. Cycl. Phot. Bac.

Aug. 19, 1987 Tushka 4710 462 54 -- -- -- -- -- 372

Aug. 19, 1987 Abu Simbel 5760 480 315 -- -- -- -- -- 462

Aug. 16, 1988 Korosko 1322 129 -- 196 -- --- -- -- 654

Sep. 9 , 1989 Tushka 2601 96 -- 3957 105 -- -- -- 261

Dec. 11, 1989 El Seboui 2337 -- -- -- 324 156 -- -- --

Aug. 14, 1991 Abu Simbel 5661 216 165 129 54 -- -- -- 309

Oct. 16, 1992 Abu Simbel 1017 -- -- 215 -- 189 109 9 --

Oct. 16, 1992 Wadi El Arab 2799 -- -- 410 -- 111 1110 24 --

Micr. : Microcystis aeruginosa Nost. : Nostoc sp.

Anab : Anabaena sp. Osci. : Oscillatoria sp.

Phor. : Phormidium sp. Apha. : Aphanocapsa sp.

Cycl. : Cyclotella sp. Melo. : Melosira spp.

Phot. Bact. : Photosynthetic bacteria

Many investigators studied the seasonal, horizontal, vertical and regional concentrations of chlorophyll a along the main channel of Lake Nasser as well as in some of the khors since the early stages of Lake Nasser filling (Fead 1980; Habib 1984, 1992a and b, 1996a, 1997; Habib et al. 1987; Mohamed, I. 1993a-c and 1996a and b; Abdel-Monem 1995). The results indicate that chlorophyll a concentration in the upper 8 m layer is high at the southern region compared with that at the northern region of the Lake. High chlorophyll a concentrations are recorded in the upper 8 m layer from March or April to October or November.

Usually, a stratified vertical distribution of chlorophyll a was observed in April-September, and a homogeneous vertical distribution in November-February. In the stratified distribution the subsurface chlorophyll a maximum was found at 2 m depth. The highest chlorophyll a concentration (42.4 mg/m3) was recorded at the surface layer in January 1984 at stn. 4 (Koroska) (Habib & Aruga, 1996), while the lowest concentration (0.0 mg/m3) was recorded at stns. 1 (El Ramla) and 3 (Allaqi) at 30 m depth in July and September 1992 (Mohamed, I. 1996b).

It seems that chlorophyll a shows seasonal changes with high values during the high temperature period and low values during the low temperature period. Furthermore, Secchi disk depth from 0.3 to 5.5 m, being high during low temperature period and low chlorophyll a concentration; and low during high temperature period and high chlorophyll a concentration. A summary of the results of some investigators is shown in Tables 47, 48, and 50 -52.

The relationship between chlorophyll a concentration and Secchi disk depth obtained by various investigators in Lake Nasser and its khors (Habib 1996a, Habib et al. 1992 & 1996; Mohamed, I. 1993a-c, 1995a & b, 1996a & b)

32

seems to be similar to those reported in other freshwater lakes (Ichimura 1961) and in marine waters (Ichimura & Saijo 1959, Saijo & Ichimura 1960, Shibata & Aruga 1982, Brandini & Aruga 1983).

I. The Main Channel (a) Regional variations. The southern region of Lake Nasser (stations 4, 5 and 6

- Fig. 4) showed higher mean annual values of chlorophyll a concentration

(about 12 mg/m3) than the northern region (stations 1, 2 and 3) (about 8-11

mg/m3). Fead (1980) recorded the highest concentration of chlorophyll a at Abu

Simbel directly preceding the annual flood. This may be partly due to the

supply of sufficient nutrient salts from upper stream of the Nile to the southern

part of the Lake and to the flood waters which push ahead multitudes of

phytoplankton to the southern part of Lake Nasser, thus resulting in the highest

figures of chlorophyll a recorded through the year. Mohamed, I. (1992a, 1993a,

1995b and 1996b) studied the regional variation of chlorophyll a concentration

along the main channel and its relation with the temperature and his results are

shown in Table 47 and Figs. 73-75.

(b) Seasonal variations. No distinct seasonal variations of chlorophyll a

concentration were observed in the northern stations (1-3), while stations 4-6 in

the southern region of the Lake showed distinct seasonal variations. The

highest chlorophyll a concentrations were recorded during summer and spring,

while low chlorophyll a concentrations were found in autumn and winter

(Table 48). The highest seasonal variations of chlorophyll a were recorded at the

southern three stations, less at the northern three stations. Levels of chlorophyll

a concentrations were generally high during the period of high water

temperature (Table 47 and Figs. 73 - 75).

The seasonal changes of the average chlorophyll a concentration in the

upper 8 m layer are illustrated in Fig. 76 (Habib & Aruga 1996). The results of

the latter authors indicate that the levels of chlorophyll a concentration were

generally high (1.0-24.0 mg/m3) at stns. 4-6 at the southern region, and low (1.0-

16.5 mg/m3) at stns. 1-3 in the northern region of the Lake. The patterns of

seasonal changes of chlorophyll a were similar among stns. 1-3 and among stns.

4-6, but the patterns at the latter stations were clearly different from those at the

former stations (Fig. 76 C and D). The range of chlorophyll a variations was

quite high at stns. 4-6 as compared with stns. 1-3. A rapid increase in

chlorophyll a concentration was observed in July or August at stns. 4-6 in 1984,

and stns. 4 and 5 in 1985 (Fig. 76-D). The same trends were also observed in

spring-early summer at stns. 1-3 in 1984 and 1985, even though the increase was

much less (Fig. 76-C). Chlorophyll a concentration was high during the period

of high water temperature and low during the period of low water temperature

at stns. 4-6 in 1984 and 1985.

33

Table 47 Seasonal, vertical and regional variations of chlorophyll a concentration (mg/m3) along the main channel of Lake Nasser. Year of Investigation and Author

1982-83

Habib

(1992a)

1983-84

Habib

(1992b)

1986-87

Mohamed

I. (1993a)

1988

Mohamed

I. (1993b)

1989

Mohamed

I. (1993c)

1990

Mohamed

I. (1995b)

1992

Mohamed,I.

(1996b)

Maximum Conc.

Value Stn. Depth (m) Date

27-24

4

0-10

Sept. 82

26.8

5

--

Aug. 84

28.2

3

--

Nov. 86

27.2

6

10

Jan.

26

5

30

Jan.

22

6

10

Aug.

17.2

5

0

Aug.

Minimum Conc.

Value Stn. Depth (m) Date

1.2 4,5,6 0-10

Nov. Dec.

82

3.0 1 --

Jan. 84

2.8 5 --

Feb. 87

0.5 6 30

Feb.

0.1 4 30

Aug.

0.1 6 30

July, Aug.

0.0 1.3 30

July, Sept.

Temp. (°C)

From 15.0 1 4

Feb. 83 29.7

5 0.0

Sep. 83

16.5 6 20

Feb. 84 31.5

2 0

July 84

16.6 6 --

Jan. 87 31.7

4 --

Aug. 87

16.2 6 30

Jan. 31.9

6 0

Aug.

14.9 6 4

Feb. 32.4

5 0

Aug.

- - - - - - - -

15.2 6 30 --

31.3 2 0 --

Stn. Depth(m) Date

To Stn. Depth (m) Date

Transpare-ncy

(range m )

From - - - - - -

- - - - - -

0.3 6

Aug. 87 5.8 1

Dec.

0.4 6

Sept. 5.3 1

Dec.

0.4 6

Sept. 5.4 1

March

0.6 6

Sept. 6.1 6

Dec.

0.3 6

Aug. 5.8 1

March)

Stn. Date

To Stn. Date

For stations refer to Fig. 4. Stn. 1 (El Ramla), Stn. 2 (Kalabsha), Stn. 3 (Allaqi), Stn. 4 (Korosko), Stn. 5 (Tushka), Stn. 6 (Abu Simbel).

Figure 77 illustrates the seasonal changes of chlorophyll a concentration in the surface water and 2 m layer at stns. 1-6 along the main channel of Lake Nasser from September 1986 to December 1988 (Habib et al. 1996). The results show that the averages of chlorophyll a concentrations were slightly higher at stns. 4-6 (1-26 mg/m3) than at stns. 1-3 (1-21 mg/m3). The seasonal patterns of chlorophyll a concentration were similar among stns. 1-3 and among stns. 4-6, even though the patterns at stns. 1 and 6 were rather obscure as compared with those of other stations. The patterns at stns. 1-3 were different from those at stns. 4-6. The range of seasonal variations of chlorophyll a concentration was high at stns. 4-6 as compared with that at stns. 1-3.

Table 48 Seasonal average of chlorophyll a concentration (mg/m3) at various stations in the main channel from October 1983 to August 1984 (Habib 1992a).

Season 1 2 3 4 5 6

Autumn 7.9 6.8 9.7 19.1 15.2 14.4 Winter 5.1 8.5 13.0 7.0 7.2 9.1 Spring 7.1 11.0 10.0 10.3 8.3 10.0 Summer 10.2 10.3 11.7 14.6 17.4 15.3 [For stations refer to Fig. 4].

34

Fig. 73 Vertical distribution of chlorophyll a concentration ( ) and water

temperature (o…….o) in the main channel of Lake Nasser during 1988

(Mohamed, I. 1993e). [For stations refer to Fig. 4].

35

36

Fig. 74 Vertical distribution of chlorophyll a concentration ( ) and water

temperature (o…….o) in the main channel during 1989 (Mohamed, I. 1993 g) [For

stations refer to Fig. 4].

37

Fig. 75 Monthly variations of chlorophyll a concentration (mg/m3) and water

temperature (C) at six stations in the main channel during 1990 (Mohamed, I.

1995b). (Temperature: (o…….o) chlorophyll a : • •) [For stations refer to Fig. 4].

38

(c) Vertical variations. High and homogenous values of chlorophyll a concentrations were recorded in the upper layers of the water column till 8 m depth. The highest values were recorded at 2 and 4 m depth because the photosynthetic activities of phytoplankton at the surface were inhibited by high light intensity of solar radiation. Thus, the highest production was obtained at about 2 m depth and gradually decreased with depth (Latif, 1974b); low values in deep layers up to 30 m were due to the depletion of light. This supports the previous conclusion of Fead (1980) that the concentration of chlorophyll a in Lake Nasser correlates with the depth of the euphotic zone suggesting that chlorophyll a is the main variable controlling light penetration into the non-flood waters of the reservoir.

In their study in October 1982 through December 1985, Habib et al. (1996) showed that the upper layer of the water column from the surface to a depth of 8 m showed high chlorophyll a concentrations; deeper layers usually contain less chlorophyll a. However, similar high chlorophyll a concentrations as in the upper layer were recorded in deeper layers at several stations in some months. Usually the homogenous type of vertical distribution was found in November through February coinciding with the low water temperature, while the stratified type in April through September coinciding with a clear thermocline which was observed during March to October (Ichimura 1961). The subsurface maxima of chlorophyll a were obtained mostly at depths 2-6 m during the period April-July. The observed maximum concentration of chlorophyll a was 57.6 mg/m3 at 2 m in November 1984 at stn. 1.

The vertical distribution of chlorophyll a concentration along the main

channel of the Lake during 1988 was studied by Mohamed, I. (1993e - Fig. 73

and Table 47). The highest concentration (27.2 mg/m3) was recorded at 10 m

depth of stn. 6 in January, and a high value (26.7 mg/m3) was found at 30 m

depth at stn. 6 in February. Mohamed, I. (1993g) recorded the highest

concentration of chlorophyll a (26.0 mg/m3) at stn. 5 at 30 m depth in January

1989, while the lowest concentration (0.1 mg/m3) was recorded at stn. 4 at 30 m

depth in August 1989 (Fig. 74 and Table 47). In 1996 (SECSF) the maximum

value of chlorophyll a concentration in the main channel (23.95 mg/m3) was

recorded in summer at surface waters at Abu Simbel, and the minimum value

(1.06 mg/m3) was found at Kalabsha at 6 m depth. During winter there was an

increase of chlorophyll a concentration in deeper water (5-7 m) as compared

with surface water. At Kalabsha and Allaqi high concentrations were recorded

compared with other localities during the same season.

Relationship between chlorophyll a concentration and Secchi disk depths. The relationships between chlorophyll a concentration and Secchi disk depth in the surface water and 2 m-layer at stns. 1-6 in the main channel of Lake Nasser during the period from October 1983 to December 1985 are shown in

39

Fig. 78 (Habib & Aruga 1996). Data are greatly scattered possibly due to

Fig

. 77

Seaso

nal

chan

ges

of

chlo

rop

hy

ll a

at

stn

s. 1

-6

in t

he m

ain

ch

an

nel

of

Lak

e N

ass

er

(Hab

ib e

t a

l.

1996).

Lin

es

are

fo

r av

era

ge o

f th

e s

urf

ace

()

an

d 2

m

()

sam

ple

s [F

or

sta

tio

ns

refe

r to

Fig

. 4].

Fig

76

S

easo

nal

chan

ges

of

A:

av

era

ge

wate

r te

mp

era

ture

in

th

e u

pp

er

8 m

lay

er,

B:

tran

spare

ncy

, an

d C

an

d D

: a

vera

ge c

hlo

rop

hy

ll a

co

nce

ntr

ati

on

s in

th

e u

pp

er

8m

lay

er

at

stn

s. 1

-6 i

n t

he m

ain

ch

an

nel

of

the L

ak

e N

ass

er.

Vert

ical

bars

in

A a

nd

B i

nd

icate

th

e

stan

dard

dev

iati

on

(H

ab

ib &

Aru

ga 1

996).

41

greater variability of the proportion of inorganic solids in suspended matter in the Lake water. If the upper levels of chlorophyll a concentration at respective Secchi disk depth are taken into consideration by assuming relative contribution of inorganic suspended solids to attenuation of light in water, the relationship seems to be exponential on a semilogarithmic plot as reported by several investigators (Ichimura 1956, Ichimura & Saijo 1959 and Ichimura 1960, Schibata & Aruga 1982, Brandini & Aruga 1983, Habib et al. 1987) in various waters.

Relationship between chlorophyll a concentration and suspended solids. The relationship between chlorophyll a concentration and suspended solids was studied for the surface water and the 2-m layer at stns. 1-6 along the main channel of Lake Nasser (Fig. 79 - Habib et al. 1996). The results indicate positive correlation between the two parameters. However, the data points were very much scattered. There is no significant difference between the relationships in the two layers.

Relationship between chlorophyll a concentration and particulate organic matter. The relationship between chlorophyll a concentration and particulate organic matter for the surface water and 2-m layer was studied at stns. 1-6 along the main channel of Lake Nasser (Fig. 80 - Habib et al. 1996). The results show that there were positive correlations with considerable scattered data points between the two parameters and no significant difference was observed between the two layers.

II. The Khors

Lake Nasser has side branches known as khors. There are 85 khors; 48 of

which lie on the eastern side and 37 on the western side. Some of these khors

are deep, narrow and with rocky bottom as Singari and Korosko. On the other

hand, other khor bottoms are relatively wide with sandy or sandy loam as

Kalabsha, Tushka and El Ramla. Some of these khors are very rich in the fish

production.

1. In Khor El Ramla. Khor El Ramla (Fig. 81) is situated at the western side of

Lake Nasser, about 10 km south of High Dam with relatively wide sandy or

sandy loam bottom. Morphology of the khor at 180 m above mean sea level

(MSL) was provided by Entz (1974a) and summarized in Table 49. Thorough

study of chlorophyll a was carried out in this khor (Habib 1992b) and the results

are summarized as follows:

(a) Regional variation. Generally, the concentrations of chlorophyll a inside

Khor El Ramla and at its entrance were higher than those outside the khor (i.e.

in the main channel and eastern part of the Lake). The mean values of

chlorophyll a concentration were about 10.8 mg/m3 inside the khor, 9.0 mg/m3

at the entrance of the khor and 7.8 mg/m3 outside the khor, i.e. in the main

channel (Table 50).

41

Fig. 78 Relationships between the transparency and chlorophyll a concentration

in the surface water (A) and the 2m layer (B) at stns. 1-6 in the main channel of

Lake Nasser. Data from October to December 1985. () Stn.1, () Stn. 2, (x) Stn. 3,

(+) Stn. 4, () Stn. 5, () Stn. 6 (Habib & Aruga 1996) [For stations refer to Fig. 4].

Fig. 79 Relationships between the suspended solids and chlorophyll a at stns.

1-6 in the main channel of Lake Nasser. () Stn.1, () Stn. 2, (x) Stn. 3, (+) Stn. 4,

() Stn. 5, () Stn. 6 (Habib et al. 1996) [For stations refer to Fig. 4].

Ch

loro

ph

yll

a (m

g/m

3)

Transparency (m) Transparency (m)

Su

spen

ded

so

lid

s (g

/m3)

Chlorophyll a (mg/m3)

42

Fig.80 Relationship between chlorophyll a concentration and the particulate

organic matter at stns. 1-6 in the main channel (Habib et al. 1996).

(b) Seasonal variation. Generally, chlorophyll a concentrations were

high in spring (March and April), decreased in autumn (October and

November) and in winter (December, January and February) in a descending

order. In autumn and spring chlorophyll a concentration inside the khor

showed the highest values compared with those at the entrance and outside the

khor but in winter chlorophyll a concentration at the entrance of the khor

showed the highest values (Table 50).

Table 49 Morphometery of Khors El Ramla and Kalabsha at 180m above MSL (Entz 1974a).

Khor El Ramla Khor Kalabsha

Distance from HD (km) 10.00 44.00

Shoreline (km) 232.00 464.00

Length (km) 23.6 47.20

Mean width (km) 1.2 --

Mean depth (m) 21.00 9.88

Surface area (km2) 95.2 620.00

Volume (km3) 2.15 7.16

Ch

loro

ph

yll

a (m

g/m

3)

Particulate organic matter (g/m3)

43

Table 50 The mean value of chlorophyll a concentration (mg/m3) in and

outside Khor El Ramla and at its entrance (Habib 1992b).

Month Inside the khor

Stns. (1-4) At the entrance of the

khor-Stns. (5-7) Outside the khor

Stns. (8-13)

Oct. 1982 11.1 5.8 4.7 Nov. 11.6 11.5 7.7 Dec. 11.9 9.7 5.8 Jan. 1983 6.7 11.7 10.5 Feb. 7.2 7.6 8.1 Mar. 10.6 7.6 9.6 April 16.4 9.0 8.5 Mean 10.8 9.0 7.8 For stations refer to Fig. 81.

Chlorophyll a concentration and water temperature at 4 stations in Khor

El Ramla for the surface water layer from September 1986 to December 1988

are shown in Fig. 82 (Habib 1995a). The results indicate that maximum

chlorophyll a concentration (i.e. 32.1 mg/m3) was recorded in March 1987 at

stn. 4, while the minimum value (i.e. 2.0 mg/m3) was in December 1988.

Generally, spring and summer showed high chlorophyll a concentrations, while

low concentrations were recorded in winter.

Habib et al. (1996) investigated the distribution of chlorophyll a at 13

stations inside and outside Khor El Ramla (Fig. 81) from October 1982 through

December 1985. The seasonal changes of the average chlorophyll a

concentration in the upper layer of 0-8 m at stns. 1-13 are illustrated in Fig. 83. It

is obvious that the levels of chlorophyll a concentration were generally higher

at stns. 1-3 in the khor than at other stations in the main channel. The range of

variations of chlorophyll a concentration was also higher at stns. 1-3 (1-46

mg/m3) in the khor than at other stations (1-20 mg/m3) in the main channel.

Trends of seasonal changes at stns. 1-3 (Fig. 83 A) in the khor were different

from those at other stations (Fig. 83 B-D) outside the khor, although the changes

at stn. 4 were rather similar to those at stn. 3. Trends of the change were rather

similar at stns. 5-13 (Fig. 83 B-D) even though the detailed variations were

different from one another. A rapid increase of chlorophyll a concentration was

observed in March, April and May at stns. 1 and 3 in the khor to attain the

highest levels especially at stns. 1 and 2. An exceptionally high value of

chlorophyll a (106.8 mg/m3 at 4 m depth) was recorded in April 1984 at stn. 2.

The levels of chlorophyll a were very high during the low temperature in

November 1984 - February 1985 at stns. 1-3 (Fig. 83 A). At stations outside the

khor, the levels of chlorophyll a concentrations were generally higher during

44

the period of high water temperature and low during the period of low water

temperature (Fig. 83 B-D). Chlorophyll a concentrations distinctly decreased in

November and December 1985 at stns 4, 6, 10 and 11 (Fig. 83 C).

Fig. 81 Location map of Lake Nasser and Khor El Ramla showing sampling

stations. Figures indicate station numbers (Habib 1992b).

(c) Vertical distribution. Generally, there were no wide variations in the

vertical distribution of chlorophyll a inside, at the entrance and outside Khor El

Ramla during any month except in March and April 1983 when there were wide

variations of chlorophyll a distribution along the water column, e.g. 14 mg/m3

at stn. 1 in March, 39 mg/m3 at stn. 1 in April, and 18 mg/m3 at stn. 2 in April

(Table 51 - Habib 1992b).

Habib et al. (1996) studied the vertical distribution of chlorophyll a concentration at 13 stations inside and outside Khor El Ramla (Fig. 81) from October 1982 through December 1985. The results show that chlorophyll a concentration was usually high in the upper layer from the surface to 8 m depth. The subsurface chlorophyll a maxima were obtained mostly at 2-6 m depth during April to August, while in other months the surface maxima or the homogenous type of distribution was observed. The patterns of vertical distribution at stations inside the khor were generally different from those at stations outside the khor. The observed subsurface maxima of

45

chlorophyll a may be related to the photoinhibition of phytoplankton

Fig. 82 Seasonal variations of chlorophyll a ( ) and water temperature

( ) at 4 stations in Khor El Ramla (Habib 1995a) [For stations refer to Fig. 81].

Table 51 The vertical variation of chlorophyll a concentration (mg/m3) in and

outside Khor El Ramla (Habib 1992b).

Month Inside the khor

Stns. (1-4)

At the entrance of the

khor-Stns. (5-7)

Outside the khor

Stns. (8-13)

Oct., 1982 3-6 1-3 1-3

Nov. 2-5 1-6 1-3

Dec. 2-6 1-4 1-2

Jan., 1983 1-3 1 1

Feb. 1-6 1-2 1-2

Mar. 4-14 5-7 2-6

46

April 4-39 3-6 2-7

For stations refer to Fig. 81.

photosynthesis at the surface layer due to high solar radiation (Latif 1974b).

According to Raymont (1980), it is common in tropical marine waters to find

out a maximum of algal growth near the base of the euphotic zone with

generally abundant light and also with high nutrient concentrations. Low

values in deeper layers down to 30 m might be due to the depletion of light.

(d) Variation in different years. The highest concentration of

chlorophyll a inside Khor El Ramla was 57.6 mg/m3 recorded in November

1984 at Stn. 1 (Habib et al. 1996). Yearly variations of chlorophyll a were

recorded during different years as follows (Table 52):

1986/1987: The highest concentration of chlorophyll a (24.0 mg/m3) was

recorded at stn. 4 in November 1986, and high values of 20.5, 20.1 and 19.9

mg/m3 were recorded at the same station in February, June and March 1987

respectively. The lowest value for chlorophyll a concentration (3.1 mg/m3) was

recorded at stn. 10 in March 1986 and stn. 11 in February 1987 (Table 52). The

high value of Secchi disk extinction depth showed low chlorophyll a

concentrations during winter, and the low value of Secchi disk extinction depth

was paralleled by high chlorophyll a concentration.

1988: The highest value of chlorophyll a recorded was 26.2 mg/m3 at stn.

4 inside Khor El Ramla at 4 m depth in April, and the lowest value was 0.8

mg/m3 at stn. 11 outside Khor El Ramla at a depth of 30 m in September (Table

52). Transparency was high at areas where chlorophyll a concentration was low

and vice versa.

1989: The maximum concentration of chlorophyll a (20.5 mg/m3) was

recorded at stn. 4 inside Khor El Ramla at 8 m-depth in December, and the

minimum concentration of 0.2 mg/m3 was recorded at stn. 11 outside Khor El

Ramla at 30 m-depth in August. A correlation was observed between

transparency and chlorophyll a concentration. When the value of transparency

was high, chlorophyll a concentration was also low (Table 52, Mohamed, I.

1993f).

1990: The maximum value of chlorophyll a concentration (29.2 mg/m3)

was recorded at stn. 4 (4 m depth) in June, and the minimum value (0.1 mg/m3)

was recorded at stn. 11 (30 m-depth) in June. The transparency was usually low

47

during the period of high chlorophyll a concentration and high during the

period of low chlorophyll a concentration.

48

Fig. 83 Seasonal changes of the average chlorophyll a concentration from the

surface to 8 m depth at 13 stations in Khor El Ramla and in

the main channel (Habib et al. 1996) [For stations refer to Fig. 81].

Fig. 84 Location of stations in Khor El Ramla (Mohamed, I. 1993f).

49

Fig. 85 Relationships between the Secchi disk depth and chlorophyll a

concentrations in the surface water and at 2 m depth for stns. 1-3 (A) and stns.

4, 6, 10 and 11 at Khor El Ramla (B) (Habib et al. 1996) [For stations refer to Fig. 81].

At station 4 in Khor El Ramla the highest values of chlorophyll a are

recorded during 1986 to 1990, while minimum values were found at stations 10

and 11 in the main channel.

Relationships between chlorophyll a concentration and the Secchi disk depths. Habib et al. (1996) studied the relationships of chlorophyll a concentration to the Secchi disk depth inside Khor El Ramla (stns. 1-3, Fig. 85). Both relationships are exponential when plotted on a semilogarithmic diagram, or hyperbolic when plotted on a normal diagram in a similar manner as reported in freshwater lakes (Ichimura 1956) and in marine waters (Ichimura & Saijo 1959, Saijo & Ichimura 1960, Schibata & Aruga 1982, Brandini & Aruga 1983). The relationships (Fig. 85) are almost similar, but the gradient of the regression line is slightly different from one to another. This difference might have been dependent on the different composition of suspended matter in the water of the khor and in the main channel (outside the khor), suspended matter should have contained more particles other than living phytoplankton in the main channel than in the khor.

Table 52 Variation of chlorophyll a concentration (mg/m3) in Khor El Ramla

during 1986-1990 (Mohamed, I. 1993 b, f and 1996a).

Year of Investigation and Author

1986/87

Mohamed, I. (1993b)

1988

Mohamed, I.

(1993f)

1989

Mohamed, I. (1993h)

1990

Mohamed, I.

(1996a)

Maximum Value 24.0 26.2 20.2 29.2

Conc. Stn. 4 4 4 4

Depth (m) within euphotic zone 4 8 4

Date Nov. 86 April. Dec. June

Minimum Value 3.1 0.8 0.2 0.1

Conc. Stn. 10, 11 11 11 11

Depth (m) within euphotic zone 30 30 30

Date March 86 & Feb.87 Sept. Aug. June

Temp. (°C) From 16 17.1 15.5 16.8

Stn. 4 6 6 4

Depth (m) within euphotic zone 30 10 15

Date June 86 Feb. Feb. May

To 28.9 30.2 29.0 30.2

Stn. 10 10 6 10

Depth (m) within euphotic zone --- 0.0 0.0

Date July, 86 July July June

Transparency From 1.2 1.3 1.2 1.1

(range, m) Stn. 6 10 10 10

51

Date Aug. 87 July July May

To 6.0 7.3 6.4 5.3

Stn. 4 11 4 & 6 10

Date Feb. 86 Nov. Feb. May

[For stations refer to Fig. 84].

2. Khor Kalabsha. Khor Kalabsha (Fig. 86) is located in the northern part of Lake Nasser, about 44 km south of the High Dam. It covers an area of about 620 km2 and its length is about 47.2 km (Table 49). Mohamed, I. (1993c) studied the regional and seasonal variations of chlorophyll a concentration in Khor Kalabsha; his results are given below:

Regional variation. The highest values of chlorophyll a were recorded at the central part of the khor (stns. 3 and 4) in May 1986 (Tables 53 and 54). Lower values of chlorophyll a were observed at stns. 8 and 9, i.e. at the entrance of the khor. The lowest value (2.6 mg/m3) was recorded at station 9 in August 1986 (Tables 53 and 54).

Generally, in both khors (El Ramla and Kalabsha) the concentrations of chlorophyll a are higher inside the khors than outside. Therefore, khors of Lake Nasser are more productive than the main channel. Moreover, southern khors are more productive than the northern. Thus, in Khor Kalabsha (44 km south of the H D) the highest concentration of chlorophyll a was recorded (32 mg/m3) compared with only 24.5 mg/m3 at Khor El Ramla (10 km south of the HD) (Table 54).

Table 53 Average chlorophyll a concentration (mg/m3) at the euphotic zone at 9

stations in Khor Kalabsha in 1986/1987 (Mohamed, I. 1993c).

Month and Date Stations

1 2 3 4 5 6 7 8 9

May 6-8, 86 16.6 9.7 31.5 32.1 26.7 4.4 5.8 16.9 13.9

Aug. 7-8, 86 7.5 4.4 8.3 8.2 7.3 7.0 -- 5.0 2.6

Nov. 20-22, 86 8.4 14.5 25.0 21.1 25.3 18.1 8.5 22.2 17.2

Dec. 28-30, 86 14.9 26.2 17.1 16.1 20.5 16.6 15.3 13.8 10.5

June 29-30, 87 --- --- 12.2 15.1 4.8 --- -- 6.0 5.4

[For stations refer to Fig. 86].

Chlorophyll a for Net and Nanoplankton

Abdel-Monem (1995) studied chlorophyll a of net and nanoplankton and

his results show that the nanoplankton (<20 m) constituted the major

component of chlorophyll a in the main channel of Lake Nasser in 1993 with

few exceptions where net plankton (>20 m) was dominant (Table 55). The

highest average values for net and nanoplankton chlorophyll a were recorded

51

in spring and the lowest in winter. The seasonal variations of chlorophyll a

were as follows:

Winter: Chlorophyll a concentrations were higher at the northern region than at

the southern. Nanoplankton chlorophyll a constituted the major component of

total chlorophyll a at all sites except at the bottom waters of Adindan. The

highest value of chlorophyll a for net and nanoplankton (8.3 g/l) was recorded

at El-Madiq at 3 m depth, while the minimum value was found at Adindan at

15 m depth.

Fig. 86 Location of stations in Khor Kalabsha (Mohamed, I. 1993c).

Table 54 Variations of chlorophyll a concentration (mg/m3) in two khors

during 1986 and 1987.

El Ramla* Kalabsha** Maximum Value 24.5 32.1 Conc. Stn. 4 4 Date Nov. 86 May 86

Minimum Value 3.1 2.6 Conc. Stn. 10, 11 9 Date March 86, Feb. 87 Aug. 86

Temp. (°C) From 16.0 °C 15.8 °C Stn. 4 6 Date Jan. 86 Dec. 86 To 28.9 28.7

Main channel

52

Stn. 10 8 Date July 86 June 87

Transparency (range,m) From 1.2 0.8 Stn. 6 2 Date Aug. 87 Aug.86 To 6.0 3.3 Stn. 4 9 Date Feb. 86 Dec. 86

* For stations refer to Fig. 84 (Mohamed, I. 1993f) . ** For stations refer to Fig. 86 (Mohamed, I. 1993c).

53

Table 55 Chlorophyll a for net and nanoplankton (g/l) [Abdel-Monem 1995].

Site Depth Winter Spring Summer Autumn

net nan. net nan. net nan. net nan.

High Dam

3 m 1.71 4.13 3.56 14.19 4.18 1.98 1.86 2.74

15 m 1.30 5.02 1.18 2.59 1.28 2.93 1.32 3.86

Bott. 1.68 4.22 0.85 1.62 0.06 0.36 1.22 0.37

Dihmit

3 m 0.89 3.88 1.07 4.11 4.21 2.64 0.09 6.02

15 m 1.08 4.05 10.63 3.68 0.78 2.64 1.67 6.11

Bott. 1.29 3.41 0.41 2.06 0.47 1.17 1.33 1.02

Kalabsha

3 m 1.05 2.85 5.84 15.16 1.27 3.67 0.53 6.41

15 m 0.46 2.21 1.23 6.06 0.27 2.66 2.10 6.02

Bott. 0.54 3.68 0.32 1.91 0.01 0.45 0.38 1.68

Maryia

3 m 0.95 2.66 1.47 7.63 0.54 3.86 0.10 7.48

15 m 0.90 3.72 12.56 6.94 2.00 3.23 2.16 6.06

Bott. 0.61 3.58 0.34 3.21 0.05 0.36 0.20 2.05

El Madiq

3 m 1.98 6.32 2.68 5.14 3.5 15.25 4.75 14.50

15 m 0.57 2.97 1.32 7.19 1.67 5.18 3.50 15.50

Bott. 2.08 6.22 2.61 2.38 0.02 0.52 0.17 1.57

Singari

3 m 0.93 3.11 19.00 16.75 0.29 8.02 6.25 20.00

15 m 0.79 3.25 8.50 17.50 0.73 2.89 4.75 14.25

Bott. 0.37 0.86 1.18 6.16 7.00 8.75 0.38 0.85

Amada

3 m 0.62 3.06 11.00 34.00 10.00 14.00 24.88 1.62

15 m 1.30 5.28 15.26 7.24 1.51 3.28 2.64 2.64

Bott. 0.53 2.36 0.49 3.23 0.12 0.55 1.66 0.39

Tushka

3 m 1.33 1.52 8.98 8.02 0.59 8.41 4.28 2.76

15 m 0.63 1.25 4.94 3.86 0.83 2.23 0.66 1.49

Bott. 0.26 0.82 1.08 2.25 0.02 0.27 0.21 0.22

Abu

Simbel

3 m 0.46 1.85 32.51 23.00 9.00 29.75 2.97 2.02

15 m 0.60 1.62 16.96 4.79 0.48 4.21 1.06 1.87

Bott. 0.30 0.84 13.87 2.89 0.80 1.45 0.03 0.30

Adindan

3 m 0.19 1.61 12.98 16.52 7.00 13.50 2.13 1.53

15 m 0.11 0.74 13.78 7.97 0.83 3.13 1.13 1.34

Bott. 1.71 1.21 3.70 3.10 0.08 0.40 0.11 0.24

Average 0.91 2.95 7.01 8.04 1.99 4.92 2.48 4.43

Spring. The highest averages of chlorophyll a were recorded in spring as well as at

most sites mostly at 3 m depth. The southern region sites attained higher

chlorophyll a than the northern ones. The maximum value of net chlorophyll a

(32.51 g/l) during the year was recorded at Abu Simbel at 3 m depth.

54

Summer: Maximum chlorophyll a values were recorded in summer at most sites at

3 m depth (Table 55). The highest chlorophyll a values were found at Abu Simbel

amounting to 9 and 29.75 g/l for net and nanoplankton chlorophyll a at 3 m

depth.

Autumn: Nanoplankton chlorophyll a was the major constituent of total

chlorophyll a at the northern sites in autumn, while the reverse was the case at most

depths at the southern region. Furthermore, higher values of chlorophyll a were

recorded at 3 m depth except at Dihmit and Mariya. The maximum chlorophyll a

value (26.50 g/l) was recorded at 3 m depth at Amada composed of 24.88 and 1.62

g/l for net and nanoplankton (Table 55).

Chlorophyll / Phaeophytin Ratio

In 1993 chlorophyll/phaeophytin ratios were calculated for net and

nanoplankton (Abdel-Monem 1995) collected from ten sites in the main channel

and the results indicate regional, seasonal and vertical variations. The following

shows the average seasonal variations of chlorophyll / phaeophytin ratios:

Winter Spring Summer Autumn

Average

values

net nano. net nano. net nano. net nano.

0.25 0.31 0.57 0.60 0.81 0.57 0.72 0.55

The results indicate minimum values in winter and maximum in summer.

PRIMARY PRODUCTIVITY

Entz (1972) reported a value of 16 g O2/m2/day for Lake Nasser from a 24 h light- and dark - bottle study. Samaan (1971) estimated primary productivity at different locations of Lake Nasser by using the C14 method, and showed that it ranged between 0.225-2.202 g C/m3/12 hrs. (Table 56). Fead (1980) recorded values ranging from 10.7 and 16.4 g O2/m2/day. During 1986/87 Habib (1998b) recorded values ranging from 1.0–27.4 and 0.7-23.8 g C/m2/day for gross and net primary production respectively.

Table 56 Gross primary productivity (g C/m3/12hrs.) at different localities in

Lake Nasser (Samaan 1971).

Site Gross primary productivity (g C/m3/12hrs.)

Surface 0.3 m 1m 2m 3m 5m

El-Berba 1.198 --- 1.486 1.284 0.797 0.295 El-Madiq 1.200 --- 1.704 --- 0.856 0.225 Singari 0.829 1.194 1.252 1.007 0.467 --- Khor Singari 1.224 1.962 2.202 1.097 0.487 ---

It appears that the Lake water is highly eutrophic and sustains a dense crop of phytoplankton. The photosynthetic activities of phytoplankton at the surface water are inhibited by the high light intensity of solar radiation. Thus,

55

the highest production rate is obtained at a depth of about 1-2 m from the surface water and it decreases gradually with increasing the depth of water.

Gross primary productivity below one square meter per day ( gross), is

controlled by the fertility of water and the depth of the photic zone, i.e. the

depth of 0.5% light illumination. The depth of the photic zone ranges between

390 cm (Khor Singari) and 485 cm (El-Birba). Results of gross primary

productivity in g carbon below one square meter per day ( gross) is given in

Table 57 which also shows the optimum photosynthetic rate (A opt.) and the

relation gross/A opt. The results indicate that the primary productivity in

Lake Nasser ranges between 3.21 and 5.23 g C/m2/day. The highest primary

productivity below one square metre is obtained at El-Madiq and El-Birba,

while the highest fertility of the water per unit volume (A opt.) is attained at

Khor Singari. The relation gross/A opt. is highest at El-Birba and then

decreases gradually towards the southern region due to the gradual decrease of

the depth of the photic zone. Habib & Aruga (1987) estimated the primary net

production at different areas of the Lake (Fig. 149 and Table 148) and found that

it ranged between 2.51-5.28 with an average of 4.01 kg/dw/m2/year. It appears

also that a gradual eutrophication of the Lake is a result of continuous

sedimentation of organic matter that accumulates on the bottom and through

the annual introduction of the flood water rich in nutrients which supply

phytoplankton with their inorganic requirements.

Table 57 Gross primary productivity below one square metre per day (

gross) in g C/m2/day and optimum production rate at different localities of

Lake Nasser (A opt.) in g C/m2/day (Samaan 1971).

Site gross

g C/m2/day

A opt.

g C/m2/day gross/A opt.

El-Birba (El Ramla) 4.840 1.486 3.25

El-Madiq 5.230 1.707 3.05

Singari 3.210 1.252 2.56

Khor Singari 4.340 2.020 2.15

In 1993 Abdel-Monem (1995) measured the primary productivity (using

light and dark bottle C14 method) and the photosynthetic capacity (assimilation

number) in the main channel of the Lake at 3 and 15 m depth at ten localities

and his results (Table 58) indicate the following:

1- The primary productivity ranged from 2.72 mg C/m3/h at 3 m depth

at the High Dam site in summer to 179.91 mg C/m3/h at Dihmit in spring

at the same depth. At 15 m depth the primary productivity ranged between

0.0 (at most sites) in winter to 128.15 mgC/m3/h in summer at Mariya.

56

Ta

ble

58

Pri

mary

pro

du

ctiv

ity

(P

.p)

(mg

C/m

3/h

) an

d a

ssim

ilati

on

nu

mb

er

(As.

no

) (m

g C

/mg

ch

l/h

) at

vari

ou

s si

tes

of

Lak

e N

ass

er

alo

ng

th

e m

ain

ch

an

nel

(Ab

d E

l-M

on

em

1995).

Au

tum

n

15

m A

s.n

o

2.4

8

0.2

6

0.2

5

2.0

1

0.4

8

0.7

5

5.6

4

2.8

6

4.6

7

31

.80

5.1

2

P.p

9.5

6

1.5

6

1.5

2

12

.19

7.4

5

10

.67

14

.90

4.2

6

8.7

3

42

.61

11

.35

3m

As.

no

11

.04

5.1

2

1.4

7

1.6

6

0.5

3

0.4

7

17

.71

7.9

1

7.3

8

19

.93

7.3

2

P.p

30

.26

30

.83

9.4

5

12

.45

7.6

2

9.3

5

28

.69

21

.82

14

.90

30

.49

19

.59

Su

mm

er

15

m A

s.n

o

7.8

9

4.4

6

24

.42

24

.50

7.1

5

0.0

0

1.5

5

0.0

0

0.0

0

12

.12

8.2

1

P.p

33

.21

15

.24

71

.54

12

8.1

5

48

.96

0.0

0

7.4

4

0.0

0

0.0

0

47

.99

35

.25

3m

As.

no

0.4

4

6.7

5

18

.48

5.6

6

0.8

0

0.7

4

0.1

2

1.3

8

0.7

7

0.5

5

3.5

7

P.p

2.7

2

46

.25

91

.27

24

.92

15

.02

6.1

6

2.8

7

12

.39

29

.38

11

.24

24

.22

Sp

rin

g 1

5m

As.

no

3.7

1

0.0

0

0.0

0

0.2

1

0.0

0

1.7

3

4.7

2

0.0

0

1.3

0

1.3

6

1.3

0

P.p

14

.00

0.0

0

0.0

0

4.0

0

41

.21

45

.03

10

6.1

3

0.0

0

28

.26

29

.66

26

.83

3m

As.

no

5.4

0

34

.73

1.9

4

11

.09

4.7

6

0.7

3

2.7

8

0.9

7

0.7

8

0.7

6

6.3

9

P.p

95

.93

17

9.9

1

40

.65

10

0.9

3

37

.20

26

.22

12

5.1

3

16

.47

43

.27

22

.29

68

.80

Win

ter

15

m

As.

no

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

10

.75

0.0

0

1.0

8

P.p

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

0.0

0

23

.87

0.0

0

2.3

9

3m

As.

no

9.3

4

0.9

1

2.0

3

9.4

9

1.4

3

2.3

5

2.2

4

4.8

8

4.7

4

2.4

0

3.9

8

P.p

45

.20

4.3

6

7.9

3

34

.26

11

.90

9.4

8

8.2

5

13

.92

10

.94

4.3

2

15

.06

Sit

e

Hig

h D

am

Dih

mit

Kala

bsh

a

Mary

ia

El-

Ma

diq

Sin

ga

ri

Am

ad

a

Tu

shk

a

Ab

u S

imb

el

Ad

ind

an

Av

era

ge

57

Comparable results were obtained in 1996 (SECSF 1996) which showed that

primary productivity fluctuated between 7.5 mgC/m3/h at 3 m depth at Abu

Simbel in autumn to 249 mgC/m3/h at the same depth at Korosko during

winter. In deeper waters (6-12 m) the range was from 45 mgC/m3/h at the

High Dam site in autumn to 247.5 mgC/m3/h at Korosko in winter.

2- The highest average annual primary productivity at 3 m depth recorded in

the main channel during 1993 was 68.80 mgC/m3/h in spring, and the lowest

value (15.06 mgC/m3/h) was recorded in winter at the same depth. At 15 m

depth the average maximum primary productivity was 35.25 mgC/m3/h

recorded in summer, while the minimum (2.39 mgC/m3/h) was found in

winter.

3- The photosynthetic capacity (assimilation number) ranged from 0.76 mg

C/mg Chl/h in spring at 3 m depth at Adindan, to 34.73 mgC/mg Chl/h at

Dihmit in spring at the same depth. At 15 m depth the photosynthetic capacity

ranged from 0.0 (at most sites) in winter to 31.80 mg C/mg Chl/h at Adindan.

4- At 3 m depth the maximum annual average of photosynthetic capacity was

7.32 mg C/mg Chl/h in autumn, and the minimum (3.57 mg C/mg Chl/h) was

recorded in summer. At 15 m depth the highest value (8.2 mg C/mg Chl/h)

was found in summer, and the lowest (1.08 mg C/mg Chl/h) was recorded in

winter.

5- There is no parallelism between primary productivity and photosynthetic

capacity. Thus, high primary productivity do not always correspond to high

photosynthetic capacity.

EPIPHYTES Epiphytic algae are among the most important food items for the tilapias

which constitute the major fish species of Lake Nasser. In Lake Nasser the

attached algae are Chlorophyceae, Bacillariophyceae and Dinophyceae.

Mohamed, I. (1993d) studied the attached algae at nine different areas of Lake

Nasser, and calculated chlorophyll a concentration and his results are presented

in Tables 59 and 60. The results indicate the presence of 14 algal species

belonging to 3 major groups (Table 59). In 1989/91 Habib (1997) recorded 28

species of attached algae at four localities in Lake Nasser.

Studying the distribution of attached algae along 9 localities indicates

that Abu Simbel, Marwaw, and Eneba are richer in number of species (i.e. 4-5

spp.) than other localities (Tushka and Allaqi 2 spp.) while other localities

contain only one species (Table 60 – Mohamed I. 1993d).

58

Table 59 Attached algae recorded in Lake Nasser during 1989-1991 (Mohamed,

I. 1993d).

Chlorophyceae Bacillariophyceae Dinophyceae

Cladophora sp. Cyclotella sp. Ceratium sp. Cosmarium sp. Cymbella sp. Peridinium sp. Oedogonium sp. Diatoma sp. Pediastrum sp. Melosira sp. Scenedesmus sp. Navicula sp. Spirogyra sp. Synedra sp.

Table 60 Distribution of the common attached algae in different areas (Mohamed, I. 1993d).

Site Attached Algae

Abu Simbel Oedogonium , Pediastrum , Cladophora and Melosira spp. Tushka Oedogonium and Pediastrum spp. El-Ramla Oedogonium sp. Marwaw Oedogonium , Spirogyra , Cladophora , Melosira and Navicula spp. Eneba Cladophora, Spirogyra, Navicula and Diatoma spp. Wadi El-Arab Oedogonium sp. Sayala Melosira sp. Dihmit Spirogyra sp. Allaqi Spirogyra and Synedra spp.

The maximum chlorophyll a concentration of the attached algae (101.4

mg/m2) was recorded at Eneba in December 1989, while the minimum values

(2.0-2.2 mg/m2) were recorded at Allaqi in July and August 1991 (Table 61). In

Tushka, the concentration of chlorophyll a of the attached algae was recorded as

82.2 mg/m2 in November 1989 (Table 61).

Table 61 Chlorophyll a concentration of the attached algae (Mohamed, I. 1993d).

Value Degree Concentration (mg/m2) Area Sampling Date

Maximum 101.4 Eneba December, 1989

High 82.2 Tushka November, 1989

Minimum 2.0 and 2.2 Allaqi July and August, 1991

FUNGI (MYCOFLORA)

Aquatic Phycomycetes from Surface Water Samples

El-Hissy et al. (1996) recorded 25 identified and 4 unidentified species which belong to eleven genera of aquatic fungi from water samples collected from Lake Nasser (Table 62). The occurrence of the aquatic fungal genera was in the following descending order: Saprolegnia, Pythium, Aqualinderella, Achlya, Aphanomyces, Blastocladiopsis, Pythiopsis, Dictyuchus, Blastocladia, Allomyces and Leptomitus.

59

The relation between the different water characteristics versus the number of

aquatic fungal genera and species is highly significant (El-Hissy et al. 1996). The

latter authors mentioned that temperature is the major factor conversely affecting

the number of genera and species with a relative efficiency of 48.13% and 36.18%

respectively. This observation is in agreement with Dick (1971), Föhn (1973),

Tomlinson & Williams (1975), El-Hissy (1979) and Rattan et al. (1980).

The total soluble salts constitute the second factor affecting the number

of genera and species with a relative efficiency of 13.12% and 19.15%

respectively and the relation is a positive one (El-Hissy et al. 1996). However,

these results are in contrast with those obtained by Scholz (1958), Fuller et al.

(1984), Amon (1978) and Amon & Yei (1982).

The pH values showed a negative correlation with the number of genera

and species with a relative efficiency of 3.32 % and 3.94% respectively (El-Hissy

et al. 1996). This agrees with the results obtained by Lund (1934). However,

many authors (e.g. El-Hissy et al. 1982, 1992, El-Hissy & El-Nagdy 1983, Paul et

al. 1984) mentioned that pH value is not a major factor governing the

distribution and occurrence of aquatic phycomycetes.

Previous studies indicate that there is no clear relationship between the

occurrence of aquatic fungi and the fluctuations in the amount of dissolved

oxygen (Alabi 1971, Rattan et al. 1980 and El-Hissy et al. 1996). However, Misra

(1980) and El-Hissy & Khalil (1989) found a close relationship between the

dissolved oxygen of water and the occurrence, seasonal changes and zoosporic

production of aquatic fungi.

The organic matter content of the tested water samples showed also a limited influence on the number of aquatic fungal genera and species (0.27% and 0.76% respectively) (El-Hissy et al. 1996).

The richest water samples in aquatic phycomycetes species were those

characterized by relatively low temperatures (15.9 - 20.3 ºC), and pH ranging

between 7.4-8.3, dissolved oxygen ranging from 5.2 to 9.3 mg/l and total

soluble salts ranging from 208.0 to 254.0 mg/l. The poorest samples were

characterized by relatively high temperatures (20.6-33.1ºC), pH values

fluctuating between 6.3 and 9.2, dissolved oxygen varying from 4.5 to 10.6

mg/l, total soluble salts ranging from 149 to 175 mg/l, and the organic matter

content between 12.0 and 51.1 mg/l (El-Hissy et al. 1996). Saprolegnia and

Pythium were the most frequent aquatic fungal genera recovered by El-Hissy et

al. (1996), whereas Aphanomyces, Dictyuchus, Pythiopsis, Leptomitus, Allomyces

and Blastocladiopsis were less frequent.

61

Vertical Fluctuations of Mycoflora

Of the mesophilic fungi Moharram et al. (1990) recorded a total of 60

species and one variety related to 22 genera from both water (48 species, 1

variety and 16 genera) and bottom mud samples (40 species, 1 variety and 17

genera) from Lake Nasser and pointed out that the fungal population of Lake

Nasser showed marked vertical variations during the period from July 1985 to

December 1986. High fungal counts were recorded at the surface waters which

were mainly due to the high counts of Aspergillus fumigatus and A. terreus.

Going deeper, the fungal population decreased till 30 m, then gradually

increased to reach its maximum at 70 m depth (Moharram et al. 1990). The latter

authors attributed such increase to the high population of Penicillium

funiculosum. At each sampling time, the water temperature and the values of

dissolved oxygen were always higher at the surface than near the bottom of the

Lake. The temperature ranged from 15 to 26 ºC and the dissolved oxygen from

1.31 to 8.98 mg/l (Moharram et al. 1990).

Table 62 Frequency of occurrence of aquatic fungi of water samples and

submerged mud samples collected from Lake Nasser (El-Hissy et al.1996 and

1997).

Aquatic fungal genera and

species

Occurrence remarks

Fungi from surface

water samples

(El-Hissy et al. 1996)

Fungi from submerged mud

samples

(El-Hissy et al. 1997)

Achlya L L

A. dubia R R

A. hypogyna R -

A. proliferoides - R

A. racemosa - R

Achlya sp. R R

Aphanomyces R R

A. laevis R R

A. norvegicus R R

A. scaber R -

Aphanomyces sp. R R

Dictyuchus R R

D. carpophorus R R

D. sterilis R R

D. monosporus - R

Leptolegnia - R

L. caudata - R

Pythiopsis R R

P. cymosa R R

P. humphreyana R R

61

Cont. Table 62

Aqualinderella L L

A. fermentans L L

Pythium M M

P. debaryanum R -

P. irregulare R -

P. pulchrum R R

P.rostratum R R

P. ultimum R R

P. vexans R R

P. thalassium - R

P. undulatum - R

Pythium sp. R R

Allomyces R -

A. arbuscula R -

Blastocladia R -

B. angusta R -

Blastocladiopsis R R

B. parva R R

Nowakowskiella - R

N. elegans - R

H = High occurrence; more than 50%, M = Moderate occurrence, between 25-50 %, L = Low occurrence,

between 12-24%, R = Rare occurrence, less than 12%, - = not recorded

Monthly Variations of Mycoflora

El-Hissy et al. (1990) recorded 51 species and one variety belonging to 21

genera of mesophilic fungi from the monthly samples of marginal water (44

species, 1 variety and 18 genera) and submerged mud (78 species, 1 variety and

30 genera) of Lake Nasser during the period from July 1985 to December 1986.

The most common species were Aspergillus fumigatus, A. flavus, A. terreus, A.

niger and Penicillium funiculosum (El-Hissy et al. 1990). The latter authors found

that the highest fungal populations were detected either in October, December

1985 or February 1986. Of the 12 thermophilic and thermotolerant fungal

Saprolegnia M M

S. anisospora R R

S. diclina R R

S. ferax R R

S. hypogyna R R

S. parasitica R R

Saprolegnia sp. L L

Leptomitus R R

L. lacteus R R

62

species, Aspergillus fumigatus and A. nidulans were common in the bottom mud

but were completely missing at the various vertical strata of the Lake.

Paecilomyces variotii, Rhizomucor pusillus, Thermomyces lanuginosus, Thermoascus

thermophilus and Sporotrichum thermophilum appeared in moderate or low

incidences in one site or more. El-Hissy et al. (1990) compared the mycoflora of

submerged mud with the one recorded from water samples, and found a high

degree of similarity.

Aquatic Fungi from Submerged Mud

El-Hissy et al. (1997) recorded 25 identified and 4 unidentified aquatic

fungal species belonging to 11 genera of aquatic fungi from submerged mud

collected randomly from the margins at different localities of Lake Nasser banks

during the period from May 1992 to October 1992 (Table 62). The richest

submerged mud samples in aquatic fungi were characterised by somewhat

alkaline pH ranging between 7.1 and 7.9 and by low amounts of total soluble

salts (1.9-2.9 mg/100 g mud sample) and low organic matter (1.6-1.9 mg/100g)

(El-Hissy et al. 1997). The latter authors showed that approximately 54 % of the

mud samples yielded only one aquatic fungal species per sample. Pythium and

Saprolegnia were the most frequent aquatic fungal genera, whereas Leptomitus

and Nowakowskiella were less frequent.

BACTERIA

Total Bacterial Counts (TBC) at 22 and 37 C

Bacteria developing at 22 C are saprophytic and their counts afford

some indication of the amount of food substances available for bacterial

nutrition and the amount of soil and other extraneous materials that water

gained. On the other hand, bacteria developing at 37 C are mainly parasitic,

derived from soil or excretal material (APHA 1975). The ratio of colony counts

at these two temperatures helps to explain any sudden fluctuation in bacterial

counts, the wider the ratio, the more probable bacteria are related to soil or

water saprophytes and therefore of minor health significance. In unpolluted

water this ratio ranges from 1 to 10, while in polluted waters, it is generally less

than one.

Elewa and Azazy (1986) studied the seasonal variations of the total

bacterial counts (TBC) at four sites in Lake Nasser (High Dam, Allaqi, Amada

and Abu Simbel) during 1974 and the drought period in 1984. Their results

(Table 63) indicate regional, seasonal and yearly variations in TBCs. Thus the

lowest total bacterial counts at 22 and 37 C were recorded in winter, while the

maximum values were in summer, mainly due to the renewal of nutrients

carried by floods and to enrichment of the Lake with organic matter as a result

of dead phytoplankton and decaying submerged vegetation. Furthermore,

63

there was a gradual decrease of TBCs from south to north, with a further

increase near the HD, which may be due to decayed materials as a result of

fisheries activities.

The results (Table 63) indicate that the total bacterial counts in 1984 increased in comparison to those recorded in 1974, being parallel with the values of organic carbon. This may be attributed to the activity of the phyto- and zooplankton, and/or relative concentration of bacterial densities related to decreased water flow from the south (Elewa & Azazy 1986).

In 1996 (SECSF 1996) bacteriological studies were carried out in the main

channel of Lake Nasser at nine sites in winter, spring and autumn. The results

of total bacterial counts (TBCs) at 22 C showed maximum values during spring

at all sites ranging from 230x105/ml at Abu Simbel to 1870x105/ml at Kalabsha.

At 37 C the range was 100x105/ml at Allaqi to 520x105/ml at El Ramla. The

minimum values developed at 22 and 37 C were found in autumn ranging

from 0.04 x105/ml at El-Madiq to 0.85x105/ml at Abu Simbel (Table 64) and

0.04 x105/ml at Amada to 0.47x105/ml at Korosko, respectively.

At the khors the total number of bacteria developed at 22 and 37 C at

surface waters in winter were higher than those recorded in the main channel.

The maximum values recorded in spring ranged from 961x105/ml at Khor

Allaqi to 330x105/ml at Khor Kalabsha near the bottom. The least number was

found in autumn, ranging from 0.06x105/ml at Khor Allaqi to 0.666x105/ml at

Khor Tushka near the bottom (SECSF 1996).

Comparing the results obtained by Elewa & Azazy (1986) in 1974 and

1984 with those recorded in 1996 (SECSF 1996) by choosing four sites for both

studies (Table, 63), the following is observed:

1. A remarkable increase of the total bacterial counts in the last two decades is

observed at all sites for both bacteria developed at 22 and 37 C, amounting to

more than 1000 folds.

2. High values were recorded, usually near the High Dam.

3. In winter 1996 there was a tendency of increase of the total bacterial count at

22 and 37 C from north to south, while the reverse was true in autumn.

4. When considering the ratio of TBCs at 22 and 37 C it was found that in 1974,

1984 and 1996 these ratios were above one, being narrower in summer and

wider in winter and spring. In 1996 the ratio was less than those estimated in

1974 and 1984, except in autumn where the ratio was much higher. Thus it

seems that Lake Nasser is still unpolluted and the low ratio values in winter

64

and spring 1996 (summer not recorded) may be due to eutrophication of the

Lake.

65

Azotobacter, N2-Fixing Clostridia and Nitrifying Bacteria

Ta

ble

63

Seaso

nal

vari

ati

on

s o

f to

tal

bact

eri

al

cou

nts

(T

BC

s) a

t 22

an

d 3

7

C d

uri

ng

1974, 1984 (

C/m

l) a

nd

1996 (

Cx10

5/m

l) i

n t

he m

ain

ch

an

nel

of

Lak

e N

ass

er

.

Au

tum

n

37

C

673

1200

0.15

383

0.12

705

0.04

637

0.31

6

(--

= n

ot

reco

rded

)

22

C

743

1800

0.22

460

0.39

720

0.44

710

0.85

Su

mm

er 37

C

2520

4400

--

2450

--

2400

--

3510

--

22

C

3730

5100

--

2700

--

2680

--

4820

--

Sp

rin

g 37

C

188

360

298

87

100

90

372

192

200

22

C

414

750

294

238

133

322

551

421

230

Win

ter 3

7

C

73

290

13

63

10

66

8.5

68

4.3

22

C

187

340

156

175

14

168

14.2

172

5.1

6

Year

1974

1984

1996

1974

1996

1974

1996

1974

1996

Sit

e

Hig

h D

am

All

aq

i

Am

ad

a

Ab

u S

imb

el

66

Counts of both asymbiotic nitrogen fixers: the aerobes Azotobacter and

the anaerobes, N2-fixing clostridia, tended to decrease in 1984, compared with

in 1974. This was attributed to the drought and less suspended matter reaching

from the south, which might carry these organisms in flood water (Elewa &

Azazy 1986).

Counts of nitrifying bacteria in 1984 showed a relative increase in

comparison to those previously recorded in 1974. This might be due to the

increase in the nitrifying activity related to the higher activity of the total

bacterial load. This is confirmed by the remarkable increase in the nitrate

content in the water of the Lake after the drought period. Thus, in 1984 the

nitrate concentration ranged from 0 to 290 g/l, as compared to 64 – 72 g/l in

1974 (Elewa & Azazy, 1986). The zero value of nitrate concentration recorded in

spring 1984 was correlated with the high photosynthetic rate of phytoplankton.

Considering pH values of Lake Nasser, it is noticed that upon storage in

the reservoir a remarkable increase of pH (i.e. 8.89) was recorded in spring 1984,

compared to pH 7.85 in autumn 1974. This may be attributed to the increasing

photosynthetic activity, consuming free CO2 from CO3-3 and HCO-3 buffer

system. This confirms that eutrophication of Lake Nasser is taking place.

Hutchinson (1957) indicated that pH of productive lakes goes parallel with

oxygen mainly in spring, the decrease in oxygen is related to a decrease of pH.

Purple Non-Sulfur Bacteria (Rhodospirillaceae)

Shoreit et al. (1989) recorded 485 isolates from different localities of Lake

Nasser in summer 1984 to spring 1985 and found that these isolates comprise 5

genera with 8 species of purple non-sulfur bacteria. Rhodopseudomonas was the

most common genus at all sites, represented by 3 species: R. acidophila, R.

blastica and R. palustris. Rhodomicrobium was next in frequency, represented by

R. vannielli only. This species was only recorded from khor sites (Fig. 87).

Rhodocyclus was represented by 2 species, R. gelatinosus and R. tenuis.

Rhodobacter and Rodospirillum were represented by one species each, Rodobacter

capsulatus and Rodospirillum rubrum. Khor sites were richer in the number of

isolates and genera of purple non-sulfur bacteria than the main body of Lake

Nasser (Fig. 87).

The superior nitrogen-fixing Rhodospirillaceae from Lake Nasser were

Rhodocyclus gelatinosus and Rhodomicrobium vannielii followed by Rhodobacter

capsulatus, Rhodopseudomonas viridis and Rhodopseudomonas palustris (Shoreit et

al. 1992). High and moderate nitrogenase activities (534 to 1528 n mol ethylene

produced/4 ml/h) were found in 56% of the isolates (total 32), while the

remainder showed low activities (76 to 477 n/mol ethylene produced /4 ml/h).

67

Purple non-sulfur bacteria in Lake Nasser exhibit seasonal and regional

distribution. Thus Rhodobacter capsulatus was recovered more often in autumn,

winter and spring 1985 than in summer 1984. Furthermore, it was more

common in khors than in the main channel of the Lake, while Rhodospirillum

rubrum was more common in summer than in winter and spring (Shoreit et al

1989). The latter authors point out that investigations are in progress to follow

changes which are expected to take place with the long storage of water and

their effect on occurrence and composition of photosynthetic bacteria.

Fig. 87 Percentage of genera of Rhodospirillaceae recovered in different

localities (Sites I and II in the main channel) (Shoreit et al. 1989).

Coliform and Faecal Coliform Bacteria In 1996 (SECSF, 1996) investigations were carried out at nine sites along

the main channel of Lake Nasser and five Khors (El Ramla, Kalabsha, Allaqi,

Site I Site II Khor El-Ramla Khor Manam

% R

ho

do

spir

illa

cea

e

Rhodopseudomonas

Rhodomicrobium

Rhodocyclus

Rhodobacter

Rhodospirillum

68

Korosko and Tushka) in winter, spring and autumn, to determine the total

number of coliform and faecal coliform bacteria. The results (Table, 64)

indicated the following:

The main channel

(a) The highest number of faecal coliform bacteria (330x103/100 ml) was recorded near the High Dam in winter. At other sites it seems that the faecal coliform bacteria were also high in winter ranging from 0.17 to 17x103/100 ml, and low in autumn (range 0.0 to 0.035x103/100 ml).

(b) The total number of coliform bacteria was remarkably high (540x103/100

ml) near the High Dam in winter. Similar to the faecal coliform, the total

Table 64 Total counts of bacteria (Cx105/ml) and the probable number of

coliform and faecal coliform bacteria (Cx103/100 ml) in the main channel and

Khors of Lake Nasser during 1996 (SECSF 1996).

Site

Winter Spring Autumn

Coliform

Bacteria

Total count at

Bacteria

Coliform

Bacteria

Total count at

Bacteria

Coliform

Bacteria

Total count at

Bacteria Faecal Total 22 ºC 37 ºC Faecal Total 22 ºC 37 ºC Faecal Total 22 ºC 37 ºC

High Dam 330 540 15.6 13 0.2 0.4 294 298 0.035 0.05 0.28 0.18

El-Ramla 0.23 32 9 8.8 0.11 0.17 1850 520 00 0.002 0.3 0.12

Kalabsha 40 46 4 3.7 0.17 0.55 1870 2.7 0.11 0.014 0.12 0.06

Allaqi 0.17 0.22 14 10 0.25 0.35 133 100 0.225 0.55 0.39 0.12

El-Madiq 0.17 2.0 0.96 17.8 0.08 0.17 572 400 00 00 0.04 0.30

Korosko 0.33 0.48 15.7 2 0.002 0.005 567 393 0.002 0.005 0.26 0.47

Amada 0.23 0.54 14.2 8.5 0.002 0.008 551 372 00 0.005 0.44 0.04

Tushka 3.3 4 8.46 3.3 0.002 0.007 447 320 0.005 0.017 0.21 0.6

Abu Simbel 17 26 5.16 4.3 0.13 0.02 230 200 0.17 0.55 0.85 0.316

Khor El-Ramla Surface

Bottom

0.2

0.9

50

54

8.6

10

35.7

57

0.008

0.175

0.05

0.02

142

200

121

133

0.0

0.14

0.002

0.225

0.58

0.06

0.14

0.10

Khor Kalabsha Surface

Bottom

3.2

9

49

90

1.33

4.1

1

3.3

0.025

0.2

0.250

0.275

777

330

393

242

00

00

0.002

00

0.42

0.44

0.30

0.10

Khor Allaqi Surface

Bottom

0.22

0.46

40

45

22.1

8

18

50.6

0.002

0.045

0.017

0.200

933

961

650

680

0.002

0.002

0.002

0.004

0.64

0.08

0.06

0.16

Khor Korosko Surface

Bottom

0.11

0.32

11

20

18.2

114

16

90

0.005

0.035

0.11

0.20

550

590

400

480

00

00

0.002

0.002

0.12

0.30

0.35

0.32

Khor Tushka Surface

Bottom

0.2

0.9

0.7

5.4

60

182

35

59

0.025

0.04

0.14

0.2

356

378

349

354

0.017

0.02

0.050

0.05

0.53

0.72

0.65

0.66

number of coliform bacteria was highest in winter at other sites but with lesser

values ranging from 0.22x103/100 ml at Allaqi to 46x103/100 ml at Kalabsha.

69

Minimum values were recorded in autumn ranging from 0.0 at El-Madiq to

0.550x103/100 ml at Abu Simbel.

The khors (a) The numbers of coliform and faecal coliform bacteria were higher at the

bottom than at the surface.

(b) In autumn certain Khors (Kalabsha and Korosko) were devoid of both types

of bacteria, and when present in other Khors they were found in small numbers.

CONCLUSIONS

Macrophytes

Eleven macrophytic euhydrophytes (flowering and non flowering) were

recorded from Egyptian Nubia pre- and post completion of the Aswan High

Dam. Two euhydrophytic species have been lost after Lake Nasser formation,

i.e. Alisma gramineum and Damasonium alisma Mill. var. compactum. Ten species

were recorded from the Lake since its filling, including 5 cosmopolitan species:

Potamogeton crispus, P. pectinatus, Najas marina subsp. armata; Zannichellia

palustris and Nitella hyalina (an alga); and 4 subcosmopolitan species:

Potamogeton trichoides, P. lucens, Vallisneria spiralis and Najas horrida. Recently,

Myriophyllum spicatum was recorded from the Lake. Three species of

Potamogeton: P. crispus, P. trichoides and P. pectinatus, recorded during the

seventies and early eighties, are no longer observed in recent years.

Najas marina subsp. armata dominates the deep water zone at most sites

and to a lesser extent in shallow water. Vallisneria spiralis dominates the

submerged macrophytes especially at Amada. Zannichellia palustris, although

widely spread in Lake Nasser but not forming dense stands, is found in shallow

waters. Potamogeton lucens is found in small stands in the northern sector of the

Lake. Najas horrida is abundant in the shallow waters of numerous khors of the

Lake, often codominant with Najas marina subsp. armata. The alga Nitella hyalina

grows in Lake Nasser not to any great depth in open sunny positions. It often

grows on calcareous sand at Lake edges.

Up to the present no floating weeds are recorded in Lake Nasser

although some of them, e.g. Eichhornia crassipes and Pistia stratioles are widely

spread both upstream and or downstream. There is a possibility of their future

appearance in the Lake and being mostly disadvantageous, so measures must

be taken to prevent their spread.

Hall et al. (1969) listed 4 species of genus Najas within the Volta Basin,

including the widespread weed Najas pectinata. The latter weed is a potentially

troublesome aquatic plant. The latter authors mentioned Eichhornia crassipes as

one of three weeds, which have caused trouble in Volta Lake (Ghana).

71

Therefore, in Lake Nasser, it is necessary to keep an eye against the

introduction (accidental or intentional) of Eichhornia crassipes. It is advised to

maintain a stock of dredgers and spraying equipment and a range of herbicides

in case of an outbreak. Rapid total elimination from the outset will save much

expense in the long run. Heinen (1965) recommended a poster campaign to

acquaint local people with the appearnce of Eichhornia.

Algae

In the early stages of Lake Nasser (1971) 27 species of phytoplankton

were recorded. During the period 1981-1993, 135 species belonging to 5 classes

were recorded: 54 spp. Chlorophyceae; 34 spp. Cyanophyceae; 33 spp.

Bacillariphyceae; 13 spp. Dinophyceae and 1 sp. Euglenophyceae.

Phytoplankton community in Lake Nasser is rich both in density and biomass.

Numerically, the standing crop increases southwards from 3.405x106 algal

units/l at El-Birba to 15.272x106 algal units/l at Adindan. The average density

of phytoplankton is 6.258x106 algal units/l in surface water; while it is

2.081x106 algal units/l at 20 m depth. The phytoplankton biomass attains

annual averages of 22.913 and 4.088 mg/l in the surface water and at 20 m

depth respectively.

Diatoms and blue-green algae are the dominant groups which exhibit

seasonal and local distribution. Diatoms preponderate mainly over

Cyanophyceae (Cyanobacteria) along the main channel and all areas as they are

well adapted to the new environment.

A marked increase of phytoplankton (upper 10 m) starting from the

High Dam (average 2.707x106 algal units/l) to Kalabsha (average 3.44 x106 algal

units/l) was recorded. Then the number of phytoplankton decreased from El-

Madiq and attained minimum values at Adindan (0.948x106 algal units/l). The

average highest phytoplankton density was recorded in August (1976), being

4.7-9.5x106 algal units/l. During flood time, flood waters push great amounts of

phytoplankton to the northern region of the Lake. At the southernmost station

(Adindan) the lowest phytoplankton densities were recorded during flood and

post-flood season.

Phytoplankton exhibit vertical distribution (during October 1979), where

the density remains, more or less, constant at the northern stations (from the

High Dam to Kalabsha). At Amada higher values were recorded at 3 m depth,

mainly of Cyanophyceae. At El-Madiq and Abu Simbel phytoplankton density

during summer and autumn was higher at surface waters compared with

subsurface ones. At Adindan, the highest density was recorded at one m depth

and the least at the surface and 10 m depth. During thermal stratification (late

71

spring, summer and early autumn) phytoplankton in Lake Nasser exhibit

vertical variations. Diatoms mainly Cyclotella spp. and blue-green algae mainly

Anabaenopsis sp. are the most dominant.

There is an inverse relationship between algal development and

dissolved nitrate nitrogen. During August (1976) Cyanophytes were most

common (71.2-89%) in the northern stations (High Dam to Amada), while

diatoms were of minor importance (2.7%). In the southern stations (Tushka and

Adindan) the reverse was the case, where diatoms were dominant (92.3-98.0%)

and Cyanophytes constituted low percentages (0.9-7.0%). Chlorophytes

remained at low concentrations throughout the Lake.

Khors sustain higher phytoplankton densities than in the main stream.

Thus, the average values were 3.622x106 algal units/l and 5.234x106 algal

units/l at Khor Kalabsha and Khor Singari respectively. Furthermore southern

khors are more productive than the northern.

Water blooms occur occasionally (1987 to 1992) in Lake Nasser, in limited

areas of the southern region. Recently it occurs intermittently all the year round

and throughout the Lake. Water blooms are caused by flourishing of

Cyanophyceae species leading to the formation of crusts and scums, where

plants die quickly and disintegrate in intense sunlight causing oxygen

depletion. In water blooms Microcystis aeruginosa is the dominant species in all

cases, followed by Nostoc spp. and Oscillatoria spp. The latter species was

recorded in remarkable quantities in Korosko, and Aphanocapsa spp. at Abu

Simbel. During the period of 1987-1992 only six water blooms were recorded.

The southern region of the Lake shows high mean values of chlorophyll

a concentrations than in the northern region. The highest concentration is

recorded at Abu Simbel in the main stream prior to the annual flood. The

highest values of chlorophyll a concentrations are recorded at 2 to 4 m depth

and gradually decrease with depth.

There is no distinct seasonal variation of chlorophyll a concentrations in

the northern stations; while marked seasonal variations are found in the

southern region. Chlorophyll a concentration in the main channel shows

seasonal changes with high values during the high temperature period, and low

values during the low temperature period. This is paralleled with Secchi disk

depth being highest during the low temperature period and lowest during the

high temperature period and high chlorophyll a concentration.

Relationships between chlorophyll a concentration and Secchi disk

depths seem to be exponential on a semilogarithmic plot, as reported by several

investigators in various waters. Positive correlation is observed between

chlorophyll a concentration and suspended solids. Positive correlation with

72

considerable scattered data points is noticed between chlorophyll a

concentration and particulate organic matter.

Chlorophyll a concentrations are generally high inside khors than at their

entrance or in the main channel, except during winter in Khor El Ramla where

the reverse is true. Khor Kalabsha located in the southern region is more

productive than Khor El Ramla located in the northern region. Chlorophyll a

concentrations in khors follow the same trend as in the main channel, attaining

their maximum values during spring and summer, and reaching their

minimum during winter. In khors there is no wide horizontal variation of

chlorophyll a concentrations inside, outside or at the entrance of khors, except

during spring (March-April), where remarkable variations are recorded. It

seems that the maximum chlorophyll a concentration in khors during

successive years (1982-1988), is, more or less constant.

Both relationships of chlorophyll a to the Secchi disk depth inside and

outside the khors are exponential, when plotted on a normal diagram in a

similar manner as reported in both freshwater lakes and in marine waters.

Nanoplankton (<20 m) constituted the major component of total

chlorophyll a along the main channel with few exceptions, where chlorophyll a

of net plankton was dominant. Maximum values for chlorophyll a of net and

nanoplankton were recorded in spring and the minimum in winter. There were

seasonal, regional and vertical variations of nanoplankton chlorophyll a. During

winter, chlorophyll a concentrations were higher at the northern region than at

the southern, but in spring the reverse was true.

Studies on primary productivity of Lake Nasser showed that it is

eutrophic with highest productivity at 1-2 m depth. Gross primary productivity

below 1 m2 ( gross g C/m2/day) ranged from 3.2 to 5.23, while optimum

productivity (A opt.) ranged between 1.25 and 2.02 g C/m2/day. The relation

between gross primary productivity ( gross) and optimum production (A opt).

- gross/A opt. - is highest at El-Birba then decreases gradually towards the

southern region due to the gradual decrease of depth of the photic zone.

Gradual eutrophication of Lake Nasser may be a result of continuous

sedimentation of organic matter which accumulates annually with flood water

rich in nutrients.

Studies on primary productivity of Lake Nasser – during recent years -

along the main channel showed that it ranged from 179.91 in spring at Dihmit

to 2.72 mg C/m3/h in summer at the High Dam at 3m depth. The highest

average primary productivity (68.80 mg C/m3/h) was recorded in spring, the

lowest (2.39 mg C/m3/h) in winter. The maximum average value of

73

photosynthetic activity was recorded in summer at 15m depth (8.21 mg C/mg

Chl/h) and the minimum in winter (1.08 mg C/mgChl/h).

Of the epiphytic algae - which constitute the most important food items

of tilapias - 28 algal species were recorded, belonging to 4 major groups :

Chlorophyta, Cyanophyta, Bacillariophyta and Pyrrophyta. The predominant

genera were Oedogonium, Stigeodonium and Spirogyra. The maximum amounts of

chlorophyll a were correlated with the dominance of filamentous forms and the

low values were observed in poor samples which contained paucity of green or

blue green algae. Spirogyra was recorded mainly in the southern part of the

Lake (Abu Simbel and Tushka).

Fungi

25 identified and 4 unidentified species related to eleven genera of

aquatic phycomycetes were recorded from surface water samples, collectd from

Lake Nasser. The richest water samples in aquatic phycomycetes species were

characterised by relatively low temperatures (15.9 - 20.3 C) and pH range

between 7.4 and 8.3. The poorest samples were characterised by relatively high

temperatures (20.6 - 33.1C), pH values fluctuating between 6.3 and 9.2,

dissolved oxygen varying from 4.5 to 10.6 mg/l, total soluble salts ranging from

149 to 175 mg/l and the organic matter content between 2.0 and 51.1 mg/l.

Saprolegnia and Pythium were the most frequent aquatic fungal genera; whereas

Aphanomyces, Dictyuchus, Pythiopsis, Leptomitus, Allomyces and Blastocladiopsis

were less frequent.

The fungal population of Lake Nasser showed marked vertical

variations. High fungal counts were observed at the surface water mainly due

to the high counts of Aspergillus fumigatus and A. terreus. Going deeper, the

fungal population decreased till 30 m, then gradually increased to reach its

maximum at 70 m depth. Such increase was basically due to the high

population of Penicillium funiculosum.

Mesophilic fungi recoverd from the monthly samples of marginal water

and submerged mud of Lake Nasser showed the highest fungal populations

either in October, December 1985 or February 1986. Thermophilic and

thermotolerant fungal species were common in one or more locality.

The richest submerged mud samples in aquatic fungi were characterised

by somewhat alkaline pH, ranging between 7.1 and 7.9, by low amounts of total

soluble salts (1.9-2.9 mg/100 g mud sample) and low organic matter (1.6-1.9

mg/100g). Pythium and Saprolegnia were the commonest aquatic fungal genera

whereas Leptomitus and Nowakowskiella were less frequent.

74

Bacteria

Microbiological studies of Lake Nasser during 1974, 1984 and 1996 showed regional, seasonal and yearly variations. In 1974 and 1984 the lowest total bacterial counts (TBCs) at 22 and 37 C were recorded in winter and maximum values in summer. There was a gradual decrease in TBCs from south to north with highest values near the HD. Furthermore, TBCs in 1984 were higher than in 1974, and those in 1996 were more than thousand fold those recorded in 1984. In 1996 total bacterial counts determined at 22 and 37 C showed maximum values in spring at all sites in the main channel and khors (no data were recorded in summer), while minimum values were recorded in autumn. In khors the TBCs of surface waters recorded during winter were higher than those in the main channel. The ratio between total bacterial counts at 22 and 37 C in Lake Nasser is more than one, with slight changes since its early filling, an indication that it is still unpolluted.

The counts of both asymbiotic-nitrogen fixers the aerobes Azotobacter and the anaerobes, N2-fixing bacteria tended to decrease in 1984 compared to ten years earlier. This might be due to the drought and less suspended material reaching from the south, which carry these organisms in flood water.

The nitrifying bacteria showed a remarkable increase in 1984 compared with counts in 1974, associated with increase in nitrifying activity related to higher activity of the total bacterial load. This led to an increase in the nitrate content of the Lake water after the drought in 1984. An indication of eutrophication of Lake Nasser is the remarkable increase of pH in spring 1984 as compared to that in autumn 1974.

Four different genera with 8 species of purple non-sulfur bacteria were

recorded from Lake Nasser. Rhodopseudomonas, the most common genus at all

sites, was represented by 3 species: R. acidophila, R. blastica and R. palustris.

Rhodomicrobium was the next in frequency, represented by R. vannielli, recorded

only from khor sites. Rhodocyclus was represented by R. gelatinosus and R.

tenuis, while Rhodobacter, and Rodospirillium each was represented by one

species. It was observed that khor sites were richer in the number of isolates

and genera of non-sulfur bacteria than the main body of Lake Nasser.

Furthermore, purple non-sulfur bacteria in Lake Nasser exhibited seasonal and

regional distribution.

Studies on the coliform and faecal coliform bacteria in the main channel showed that their number was highest in winter near the High Dam compared with other localities. In other sites the highest values were recorded also in winter (no records were undertaken in summer), while minimum values were found in autumn. The number of coliform and faecal coliform bacteria at the bottom of khors was higher than those at the surface. Furthermore certain Khors (Kalabsha and Korosko) were devoid of both types of bacteria.